I own the 54TX and M60s.. I have a sub, but that is because I am a movie freak.
Audio is good with the M60s and there is a good amount of lower frequencies coming out of the M60s but I have learned that the speakers themselves were more th culpret than the receiver. Just moving the speakers so that they were a foot or so away from the wall (but not too far away) helped with the bass levels.
With that said, the speakers do need to be set to large in the 54TX. They were defaulted to small when I got my 54TX, and after running the MCACC it put them to large, put the manual setting of this is also very easy to do. That helped too.
I almost always listen to audio with the sub on, but not because of something lacking in the M60s but because I like bass, and I listen to music that had a lot of low frequency and bass elements that without a sub wouldn't be there no matter what speakers I was using. I'm not talking rap or anything, but I do like the "feel" I get of the sub. It makes it feel more like being at a concert where the bass is cranked up.
