Downloaded and hi res music breathing

Hello out there, I'm new to all the hi res stuff coming out, so thought I'd walk into it before running. I know many of you out here are way more advanced than I, so I'm also hoping for some help. Anyway, the problem I'm having is while hi def music is played, whether it be streamed or downloaded, it sounds like my system is breathing. The sound is normal then goes slightly softer. It's annoying as hell. The sound card I'm using is an Asis Xoner Essence St with a Transparent digital coaxial played through a Proceed AVP-2. This doesn't happen with any other music sources. The audio card is brand new, I don't know if it's a setting I have wrong or does it sound like a bum sound card. Please advise and thank you in advance. Joe
I'm not sure I get what the problem is. Does the music keep changing in volume or is it something else?
I have used the PCI version, so some questions from my experience using it

1) the card actually requires a separate IDE type power connection. Have you verified that the power supply in your PC meets the combined stated power requirements of the load of MB, CPU, video card, audio card, and attached peripherals?

2) do you have the latest driver/control panel downloaded from Asus? this card is finicky, you need the manufacturer drivers as it doesn't work right if you use windows default plug and play

3) have you checked the control app to make sure all effects are turned off? This probably doesn't matter for SPDIF but just to be sure... I believe you also can set the speed limit for SPDIF here but can't verify since I don't have the card installed any longer.

4) is the PC optimized for audio? The Asus is not a particularly efficient processor (gaming slows down with it)and if you have lots of background apps they may be interfering. There is an audio optimizer app called Fidelizer, you may want to try it's options. It basically shuts everything down you don't need for audio with varied stages, the penalty is that you have to reboot to go back to normal. If one of the stages resolves the issue, you know it was a resource contention issue.