I've done some tests
http://www.satbythesea.com/vacard_cputest.pdfMy findings for what they are worth...
Playback of MP3 is less CPU intensive than APE (I use max compression APE so that may explain why)
ASIO drivers use less CPU than DirectSound
I struggle to imagine anything better in quality than ASIO as it sends the same signal as you would get between a CD transport and a DAC (I think). It certainly avoids Microsoft software (like mixers, DSP, etc) getting in the way of the audio signal
I use APE > ASIO > HiFi DAC or Lossless WMA > ASIO > DAC
APE is a big CPU overhead if I use my virtual/software soundcards (which converts to MP3 on the fly) in order to stream the output to networked audio
:-\I struggle to tell the diffrerence between my HiFi DAC (£2,700) and my soundcard DAC (M-Audio 24-96 - £150) !!!!! sad isn't it - boys toys and besides the DAC has lights and buttons!
I can definately tell a significant difference in quality with APE over MP3 and so for me the CPU overhead is worth it
As a HiFi geek the less in the way of the signal the better - so ASIO and an external DAC lights my candle
Hope it helps!
CPU is pretty important - I struggle to run 3 zones playing back APE on a PIV 2.4GHz with 1.5Gb RAM!