Ok here is what your mix looks like:
http://dl.dropbox.com/u/10584477/Before.jpg
Over all the frequency plot is quite flat (a good thing in metal), and you can here that when you listen to the track. I noticed straight away that there was some major sub low end pumping through on your kick sample/s and you can see this in the above graph peaking at round the 45 - 50 hz mark and going down as low as 30hz. This is what you here when you listen on other stereos and it is also what is likely to be responsible for you not 'getting you loudness'. You need to low shelve the kick samples at round 100hz -1db to -1.5db and high pass anywhere between 30 and 50hz to solve this problem. You will then find you can put some lows/mids back into you guitar and bass that you may have removed to try and fix this problem.
Next is a graph with 2 songs overlayed. Your song being the bold colored lines, and a professional mix of a well known band mixed by someone on this very forum in lighter colors in the back.
http://dl.dropbox.com/u/10584477/Image-overlay.jpg
To begin with they look vastly different but in fact they are not really. The height difference is the difference in loudness. Look at the bottom end. You will see the big hump in your track compared to the commercial track. The only other small differences is the dip in between 80 - 200hz (could be from you removing low end from guitar and bass as mentioned above) and the dip round 500hz.
Lastly, here is an overlay of your track in the background and a re-eq'ed version of your track I did to show you where the possible issues are.
http://dl.dropbox.com/u/10584477/before-after-overlay.jpg
And here is a sample of your track with the EQ applied.
http://dl.dropbox.com/u/10584477/Rough mix_eq.wav
It may sound a little less 'hyped' than the original but that is ok as it should translate better and alow the playback source to provide the 'hype'. This will also be able to be pushed louder than before.
Now, I re eq'ed an already mastered track so I am not saying it is now mint or sounds better or what ever, it is just a crude example. And, what I would typically do now is to go back to the mix and fix the problem discovered in mastering rather than try to fix it with mastering because adjusting the overall frequency plot effects all the instruments in the mix potentially causing new problems or imbalances, whereas going back to the mix will fix the issue with out adversly effecting the rest of the mix. Because of this the eq I did may not sound as pleasing as creating a mix that has the same plot before mastering eq. (if that makes sence)
Hope this makes sence and helps you out M8.
Cheers,
Nigel.