please do not use asm, only pure object pascal code please! That way we keep the project open for compiling on mac os. (yes there is an object pascal compiler for mac-osx!)
Mixing is done using openal. (multiple source). Also no mixing should be done by software. OpenAL wil use hardware-mixing when available.
It makes things harder to program, but the end result will be better, both in speed and portability.