i can lol on pc and ableton users 
is amazing to read things from people who doesnt even know what they r talking about, thats funny
obviously is full of vst about mac softwares, and they are the best, much better than pc, even coz on mac and using logic, u can use the AU VST (Audio Unit System, created by Apple for logic users, and r amazing!!!), that other softwares or OS cant use....
the problem is that, about what u wrote in the question, i guess u dont need a vst but a plugin, as a vst is to MAKE sounds, but a plugin is just to modify and not to create... so if u already have a bass (as u wrote) and want add something on it, u need to use a plugin, and there are a lot on mac, than it depends about what kind of software u use....
cubase and logic are the best softwares and not ableton, so keep in mind the VST system had been create by Steinberg, same creators as cubase, so all other softwares just use what they invented, it is already a point to think about... ;-)
another thing is that other softwares, as Ableton (poor for me!!!), still use the VST (1), but the latest version of cubase is already using the VST 2 and 3, maybe cubase 7 reached VST 4 already but im not sure about it...
FL is much better than ableton, amazing dynamics and amazing sound, but i will be always a cubase user as cubase is a master software, and ableton, FL, and reason, are slaves, it means that inside my cubase i can use in rewire all other 3 mentioned softwares, but u cant do the opposite as they are slaves so they cannot have other softwares inside...
now lets go to ur problem.... if u need just to modify a sound u already created, in this case the bassline, u just need to add 1 or more plugins to ur track line, for example u can use one of this:
First u need a frequency analyzer to check frequencies and make a correct job when changing the bass, than u can add a BASS RIDER, or a CLA BASS, or a KRAMER BA, or a JJP BASS, or a MASERATI B62, or a MAXXBASS, or a RBASS, and so on.... there are a lot, so dont listen to people who doesnt know things, they r just ignorant about VST and softwares!!!
PS: other big differences between cubase and other softwares, are that on cubase u can export files in all formats and choose even the quality, u cant do it in other softwares as ableton, so if u need to publish a track on soundcloud, with cubase u just export the track in the kind of file u prefer, choosing the quality, for example, u dont need to wait more time to export a wav so u can export it directly on mp3 at 192 kbs, to dont give to the people the best quality in case they can DL ur track using softwares... with ableton u must export on wav and use another software to make it on mp3, so so so long and useless for a "supposted" professional software... another big missing in other softwares is that, when u finish a track and u must make the mixdown or mastering, u must analyze the track to check things as volume peaks, channel notes, DC OFFSET, and other things u cant miss to make a proper mix and master, with ableton u must export the track as i said before, and use another software to check this things, but with cubase u can just right click the interested track and click on statistics, so in few seconds u can know all what u have to know about ur track ;-)
never forget that cubase is the FATHER of all softwares, everything comes from steinberg and from cubase, since ever!!!
is amazing to read things from people who doesnt even know what they r talking about, thats funny
obviously is full of vst about mac softwares, and they are the best, much better than pc, even coz on mac and using logic, u can use the AU VST (Audio Unit System, created by Apple for logic users, and r amazing!!!), that other softwares or OS cant use....
the problem is that, about what u wrote in the question, i guess u dont need a vst but a plugin, as a vst is to MAKE sounds, but a plugin is just to modify and not to create... so if u already have a bass (as u wrote) and want add something on it, u need to use a plugin, and there are a lot on mac, than it depends about what kind of software u use....
cubase and logic are the best softwares and not ableton, so keep in mind the VST system had been create by Steinberg, same creators as cubase, so all other softwares just use what they invented, it is already a point to think about... ;-)
another thing is that other softwares, as Ableton (poor for me!!!), still use the VST (1), but the latest version of cubase is already using the VST 2 and 3, maybe cubase 7 reached VST 4 already but im not sure about it...
FL is much better than ableton, amazing dynamics and amazing sound, but i will be always a cubase user as cubase is a master software, and ableton, FL, and reason, are slaves, it means that inside my cubase i can use in rewire all other 3 mentioned softwares, but u cant do the opposite as they are slaves so they cannot have other softwares inside...
now lets go to ur problem.... if u need just to modify a sound u already created, in this case the bassline, u just need to add 1 or more plugins to ur track line, for example u can use one of this:
First u need a frequency analyzer to check frequencies and make a correct job when changing the bass, than u can add a BASS RIDER, or a CLA BASS, or a KRAMER BA, or a JJP BASS, or a MASERATI B62, or a MAXXBASS, or a RBASS, and so on.... there are a lot, so dont listen to people who doesnt know things, they r just ignorant about VST and softwares!!!
PS: other big differences between cubase and other softwares, are that on cubase u can export files in all formats and choose even the quality, u cant do it in other softwares as ableton, so if u need to publish a track on soundcloud, with cubase u just export the track in the kind of file u prefer, choosing the quality, for example, u dont need to wait more time to export a wav so u can export it directly on mp3 at 192 kbs, to dont give to the people the best quality in case they can DL ur track using softwares... with ableton u must export on wav and use another software to make it on mp3, so so so long and useless for a "supposted" professional software... another big missing in other softwares is that, when u finish a track and u must make the mixdown or mastering, u must analyze the track to check things as volume peaks, channel notes, DC OFFSET, and other things u cant miss to make a proper mix and master, with ableton u must export the track as i said before, and use another software to check this things, but with cubase u can just right click the interested track and click on statistics, so in few seconds u can know all what u have to know about ur track ;-)
never forget that cubase is the FATHER of all softwares, everything comes from steinberg and from cubase, since ever!!!
