About hearing the bass parts... go download Audacity, it is free. Then use the filters to filter out everything but the bass part and put the bass up to +12db. You should be able to hear it then! As an added bonus, Audacity contains a FFT that can tell you the frequency spectrum of a particular passage. You can use that to determine the key and even specific notes if you select a small enough sample. It also can slow the tempo without changing the pitch for those particularly hard passages.
Have fun!
Ox.
PS: I am in no way affiliated with the Audacity project except as a user. Even if I was, its free, so what would I gain?!