ASIO for all has nothing to so with polyphony, unless your using soft synths. Which is simple, add another softsynth to your project for more polyphony..
If your asking how to curb some of the 'note stealing' with kX Synths... try:
Settings/Synth Compatibility/Legacy Realease/Decay. - It helped with me... but, just in the case of decays 'stolen' or truncated... your limited to 64 oscilators IIRC - its a hardware thing... but yes - kX handles 'hardware' (hardware accelerated software) synths differently than CL drivers (better imho) - but have noticed occasions kX note stealing to be more 'noticiable'. My idea on this is from a different algo for channel priority... but its just an idea, I cant prove or disprove it.
For a fast solution, use the free SF player VSTi for more polyphony, and a little better fidelity for SF's.
(oops - it appears their site is down)
http://www.rgcaudio.com/sfz.htm
Maybe its temporary...???
ASIO4ALL - is used if you dont have an ASIO driver already (its an ASIO to MME/WDM emulator/interface type of thing that gives me too high of latency for me to use, tho others post that they do use it for 24/96 on cards with the Wave HQ device??)