I have a noob question here.
I have a 5.1 card installed in my pc and I am using the optical out to go to my 7.1 onkyo reciever. Is the 5.1 card ok to use or do I need to buy a 7.1 card to use with my 7.1 reciever to get true 7.1 sound.


Thanks for any help in advance!

Using the optical out suggests that your card is sending the program bitstream to your receiver with out doing any Dolby processing. If that's true, then your receiver will do the decoding of whatever Dolby type is present.

Why not just connect it up and see? I think all of the more recent Onkyo AVRs display the incoming signal type.

At present, most (all??) 7.1 sound is created by the processor anyway. So, 5.1 output from the pc can be matrixed to 7.1 by the receiver. The only thing you'd miss out on might be something coded with the EX or ES flag (6.1). This would be output as 5.1 and matrixed to 7.1 as well. Not sure what, if even anything, you'd be missing in the case of a 6.1 encoded movie.

I doubt the 6.1 info would be lost, but I really can't explain very well what the sound card does with the extra info and how the original 6.1 source would compare sonically with the resultant 7.1 matrixed output.