Hello,

I use a Mac Mini HTPC to play videos and music, and a PlayStation 3 for BluRay. Both are connected to the 990 with TOSLINK fiber optic digital audio cables. The 990 drives 5 2200 monoblocks to my speakers (I don't need / have a sub).

One thing I don't quite understand is the 990's Surround Mode setting. For example, consider the scenario where I'm playing a DVD on my Mac Mini. As I understand it, the DVD's audio track is encoded in Dolby 5.1, and the 5.1 audio data is streamed to my 990 over the fiber optic cable.

Given that, what is the difference in selecting 5 STEREO, BYPASS, or PLII MOVIE? It seems like 'bypass' would let the unadulterated 5.1 audio signal come through as the director intended, and the other settings would apply some kind of possibly-unwanted coloration.

Or another scenario is playing a video game on my PlayStation 3 -- the sound generated during gameplay takes advantage of 5.1 surround, so do I want to use 'BYPASS' on the 990's optical input to avoid mucking with this?

Obviously I don't fully understand what is going on, so I'm hoping someone can please help me grok this concept.

Thanks!
-Jeff

The "Surround Mode" function in the setup menu is of limited purpose, in my opinion. I prefer to use the surround mode buttons on the remote to select the preferred mode when a certain source format is playing. The Model 990 remembers these preferences separately for each input.

Each mode provides different surround processing. The manual explains these modes very well, but here's a quick summary of the ones you mention (there are a lot more, depending on the input signal):

Bypass: This mode is only available with stereo modes, and it is really best suited for stereo analog inputs (which then "bypass" analog-to-digital and digital-to-analog conversions).
5 Stereo: This mode expands a stereo source to five speakers while retaining the stereo source. Left channel is copied to left surround, right to right surround, and a combined signal goes to center.
PLII Movie: This is Pro Logic II (Movie). It is a Dolby program that generates a five-channel signal from stereo sources.

Note that all three modes you listed are only available when you have a stereo source playing, not a 5.1 source. They are also modes that suggest you have a 5.1 speaker setup, as there are other modes available for 7.1 setups. As a result, when a 5.1 source is active, you will not have many choices available. You will have Dolby Digital or DTS (depending on what the 5.1 source is), Upsample, and maybe a stereo downmix mode or two. The "bypass" mode won't be an option and isn't applicable.