Sound
ALSA
Gentoo has a guide for ALSA, but I did not know about it until after I got my sound card working. Installing ALSA was incredibly easy for me, but I would imagine that this was so because I already had the pre-requisites fulfilled. Make sure your sound card is supported by consulting this table. I simply followed the directions for via-82xx, my chipset. After I did emerge alsa-driver alsa-xmms alsa-utils and inserted the relevant modules, my sound was working. In order to get sound working after reboots, I had to edit /etc/modules.d/alsa appropriately and add /etc/init.d/alsasound to my default runlevel. However, I was unable to get SPDIF output functioning. Please tell me if you can do this and how for the via82xx.
Gapless music
It's unacceptable when I play some mp3s/oggs that are seamless when transitioning between songs. Live music or mixes are good examples. Fix this by installing xmms-crossfade.
Controlling xmms with an IR remote and LIRC
After I picked up an el cheapo packard bell serial receiver, I programmed the accompanying remote with my Onkyo stereo remote to be able to control xmms. Thus, I can skip songs, select songs, pause, and other common xmms functions with a remote control. I would advise against purchasing my serial receiver because the range is limited, but I hear irman receivers work well. You may also consider rolling your own home brew hardware. Consult the lirc website. The next step is to install lirc and the xmms-lirc plugin. Good luck. This was not easy for me. However, the documentation for lirc is very thorough. Even though I only use lirc with xmms, lirc is extremely flexible in that it can control many other applications as well, like mplayer. Let me emphasize how cool controlling software with a remote is. I find it especially convenient that I point one universal remote at my stereo to control mp3s, CDs, DVD, etc.