Do you use the optical output or the multi-channel output of the sound card? My current receiver does not support the high bit rate formats and I want to buy a new one, but I understand that the SPDIF optical output does not support HBR. Is that true?
Correct that SPDIF does not support the new optical formats. I can't tell you what the exact numbers are for throughput but I'm sure you could find them with some looking.
Since these are out of the question, it really doesn't matter how you connect your components. Obviously connecting a 5.1 setup would be a lot cleaner using the single cable. That should be the only difference that you notice between the two options.
I currently use the optical connection because, like you said, is cleaner. But I was thinking that I could let the HTPC do all the decoding (Power DVD Ultra can decode all the lossless HBR formats) and use the receiver as a simple amplifier. I will have to connect each individual channel separately to the receiver and the installation will be messier but I will have the best possible sound.
I use LPCm through HDMI (Intel G35 chipset) to get lossless audio to my reciever but if your AVR doesn't handle audio over HDMI then yes to get lossless audio then you would have to go the analogue route ....the protocal for HD audio isn't supported by by SPDIF and never will be (the bandwidth is sufficient however) so you are limited to ~1.5Mbps dts or 640Kbps DD. Hope that helps.