Darren, I listened to those two songs on your site. The first one has a lack on the bass, not only the bassguitar, but as well for the kickdrum. The second one has a firm kick, abit too firm if you'ld ask me. The bass guitar is a bit harder to judge because of too much of kick that covers up the bass notes. But for both mixes I would think it must be your monitors or the accoustics as Matt allready mentioned as a possibility. The question is, coming from this conclusion, how did it happen that one song lacks of something that the other has a bit too much of (at least in the kick). It seems to me that you used two different methods. Maybe nr one was created in BB where you can only have one EQ for all instruments, so cutting all base for the audiotracks inside and used the seperate EQ's in RB for the second song? Just a wild guess...

I'll be back...