By default, DSL loads the "kahlua" driver for sound on the T20, but that doesn't work. What does work is the soundblaster driver, but it needs an option!

Add these lines to /opt/, somewhere near the end, perhaps:

# setup audio driver for Evo T20
modprobe sb mpu_io=0

Restart DSL, and now you can play your favourite mp3 like this :-)

$ mpg321 "Vengaboys - Boom Boom Boom Boom.mp3"

Where did I learn this? Dag Sverre Seljebotn told me:

Well I can help you here, I have sound working on my T20s. What I do
using LTSP is passing

    sb mpu_io=0

as the sound module parameter. That is using OSS and the 2.4 kernel, but
the main point is
a) It emulates a soundblaster
b) You need to turn off MPU

and with that you should be on your way with 2.6 and ALSA as well. I
didn't specify any irqs/dmas so autodetection seems to work.

If you plan to run X at the same time then you must turn on "NoAccel" in
order to avoid crackling (or you can try to turn on PciRetry instead).

So far, I've not noticed a problem with crackling, but I've done little testing.

Bartek Szurgot is successully using this option:

modprobe sb io=0x220 irq=7 mpu_io=0x300

As a vague performance indicator, I have used the T20 to play mp3 files off an SSHFS mount from another networked computer (because that's where the files where). The files were encoded at 128kbps. CPU usage was about 20% - this includes mp3 decoding as well as the ssh decryption.