smeagle,
First of all, I assume that you have correctly calibrated the channel levels/delays and the subwoofer, using an SPL meter (if not... well, I have no comments.
).
1. Yes, something is clearly wrong here. Does it "hiss" only in the surround mode? When you switch the receiver into the Stereo or Direct mode, does it subside? How about the Dolby Digital mode vs. matrix surround modes such as DPL II? Also, does it still "hiss" when the CD/DVD playback is stopped? How about when you switch off the X-Box altogether (and with various listening modes on the receiver)?
2a. This could be the character of the M22/VP100, if it isn't grossly bad and it depends on CDs. What is the floor material of the room? Do you have flat, hard surfaces in the room (e.g. concrete walls, big glass windows)?
2b. Again, this could be inherent to the M22/VP100. What's the distance between the M22's? How much are they "toed in"? How far are the M22's and VP100 placed from the walls?
2c. What is your subwoofer crossover frequency on the receiver? Is the crossover circuit on the EP175 correctly defeated? Have you tried both phase-switch positions on the EP175? Are all speakers set to "small"? Have you tried several different locations for the sub?
Enough questions for now...
