I am using libSDL_1.2.6-zports-5_arm, libSDL-net_1.2.5cvs-1_arm, lib SDL-mixer_1.2.5cvs-1_arm on my sl6000. No problems that I have noticed. I have prboom_2.2.3-2_arm working with these libs. Also have the midi sound working in prboom with timidity installed.
I would be interested in hearing what SDL libs others are using on their sl6000's.