Do I need ASIO for Windows 7 ?

Windows XP and ASIO works just fine. If you are just sending PCM out a USB port there's no reason for anything as long as you configure your "player" correctly. Foobar can be configured not to change the bitstream, same for J. River Media player.

I'm assuming your using .WAV files or lossless compressed files, eg. FLAC. There's not much to reading a file, decompressing if necessary, and sending it out a USB port.

Schwinnindia...I'm years removed from running XP anything so I can't help with how an XP system sounds. However, I would feel very RAM limited with XP. The better players load into memory for a better delivery. With Win7 you can easily do an 8GB RAM system and with J River Media Center it's a very solid playback system for 24/96 and 24/192 files.

Have you looked at system latency with WASAPI when comparing J. river 'play from memory' option. Streaming over LAN with WASAPI gives incredibly low latency (I have SSDs on bothe server and client), whereas dumping everything through memory causes a bit of a jump and can even strain the latency when doing 192kHz.

When I moved my T60 laptop from XP to Win 7, I noticed a huge improvement in sound quality. I was using Foobar2000 on both operating systems, but just kernel streaming (ASIO4ALL was too buggy for me) in XP and WASAPI in Windows 7. I confirmed with an external box that XP was re-sampling everything to 48kHz, and Windows 7 with WASAPI keeps the native file sample rates for output. Listening was all through a headroom ultra desktop amp whose DAC was fed S/PDIF from the laptop dock. It has an ASRC but is still sensitive to jitter, which is probably also better with WASAPI, in addition to the lack of re-sampling.