The first part of this is an addition to my earlier post on audio in Ubuntu. If you want a bit more detail about what you're doing with that fix then check out the original source, which also has some other useful links. After applying the fix I had problems with my sound crackling rather more than I like to hear. If you have similar problems then check out the Dmix page on the ALSA wiki, specifically the "Still Hearing Stuttering?" and "Comments" sections near the bottom. I haven't tried that extra modification myself (I was in the middle of something at the time and just disabled mixing again), but it looks promising and easy to do. That page is a goldmine of information about modifying your setup so it may be worth taking a bit of extra time to read through.
Ok, with that out of the way, how about visualisations in Rhythmbox? I use that as my audio player and I'm quite happy with it except it only has two visualisations available (I don't use them much, but they do amuse me so I like to have a few). Luckily information on this is easy to find and it turns out you need to install the libvisual-0.4-plugins package. I had a slight problem with one of them causing Rhythmbox to crash, but that may just be my setup as I don't recall seeing any warnings.