I am running a Vista Media Centre through a Cambridge Audio Azur 540R v2. The sound is processed by the ASUS motherboard's onboard Soundmax chipset & piped to the receiver using coax SPDIF. I have noticed that when a song's quiet intro gives way to the presence of the full band the backside drops out of the sound leaving it weak & muffled. The source is 320Kbps MP3. When I tried the DTS version of the same music the problem was not evident. The same MP3 sounds great on my main PC, on MP3 CD in my car & on my Creative Zen. For technical reasons I have yet to try the CD version for comparison. I am also planning on trying alternative front speakers but surely if it were the speakers at fault then this would carry through on the DTS version too? I have already upgraded the amp from Yamaha RX-V359 to CA Azur 540R v2 as had been recommended elsewhere. Does the MP3 get converted to analogue & then back to digital by the PC to pipe thru the SPDIF? If so could it be this double conversion that is blowing out the quality? If so what can I do to fix this? New soundcard? Any recommendations?