most of the nice freeware ampsims aren't suited for mac because the programmers don't own a mac,
but you can use every ampsim for guitars, Ola for example likes the ultra shitty distortion on bass
even the integrated sims in most of the daws can work pretty nice on bass.
I think I am the only one who read that he's a Mac User
But like I said, just use a plugin for guitar, high pass it and mix it with a compressed DI and you're finished.
Now Im working on an Intro for a client and Im using:
Audiffex Gallien Krueger Amplification (Dirty channel of 2001RB amp with any overdrive pedal for extra boost)
blended with
Audiffex ampLion Free (Dual Recto amp).
Had a lot of fun with Audiffex products (especially with advanced speaker management - mic type, 3D positioning, angle, distance, etc.)