I was able to use the Dolby Headphone VST to downmix to two channels. I then tried to send to a second instance of JRiver via the WDM driver for 2 channel output. It played fine, but whenever I disabled the Dolby Headphone plugin in a zone in one instance, it also disabled it in the different zone in the other instance of JRiver.
The only way I could come up with for it to work would be to use Convert Format twice: once to use Dolby Headphone and the second time to downmix 5.1 with muted surround channels to stereo using JRSS. Now you can play the converted files along with the stereo files in a single playlist with USB output to your DAC. Then you could try the Binaural Surround VSTs from Blue Ripple. Hmm, I can't remember now if VST's work yet in Convert Format and don't have time to test right now.
Well as I said, that is one example. I could come up with ten other examples which would use this Zone Grouping system just as easily.
You cannot use a VST to do virtual surround in Media Center, because Output Format is fixed to the top of DSP Studio, it controls the signal sent to the playback device and mixing is linked to the channel output, so if you are playing to a 2 channel DAC it downmixes the 5.1 source to 2.0 before it reaches the VST plug-in.
And you can maybe kind-of hack it in by disabling Output Format, having the VST plug-in mix that down to 2 channels, send out a 5.1 signal to a virtual device and then route it back into MC and drop the additional channels before sending a 2 channel signal to your DAC, but that is a ridiculous setup which is going to be very unreliable.
It doesn't actually get around the fact that I would still need two separate zones configured to handle 2.0 and 5.1, since I want an untouched output with 2.0, while 5.1 gets virtual surround.
The system that I have in place works, it's just that I am stuck managing separate playlists for stereo and multichannel content, and manually switching tabs depending on where a file plays.
I do use the WDM driver for things like live video streams, where being able to mix it down to mono, filter out certain frequencies, and apply dynamic range compression are far more important than actual audio quality, but the WDM driver is not suitable for high fidelity reproduction right now in my opinion. It's far too prone to drop-outs for one thing. (pops and clicks during playback)
I have also tested a number of VST plug-ins for virtual surround in other applications (where output channel config is the last step, and separate from mixing) and the only one which produced good results in my opinion was Dolby Headphone.
I have contacted Blue Ripple Sound about their binaural surround VST because I am sure it will do a good job (their OpenAL game driver is great) but that is a very expensive product and there is no way of getting that to work properly in MC due to everything I have described above.
And I've already gone out and bought the sound card after exploring all these options. Of all the virtual surround products that I have tested - which is a lot of them - Creative's SBX Surround gave the best results regardless of price or complexity of setting them up. Of the ones I'm aware of, the only things I haven't been able to try have been the Smyth Realizer and that BRS Plug-in.
I would love to have the option of using Dolby Headphone though, because while I prefer SBX for games/movies, the results with DH2 were quite good for music.
I haven't had much luck getting VST plug-ins to work with MC's conversion options. Some of them do work, but it's been very hit-and-miss.
And I don't want to be converting files. I could do that externally in another program right now. (and have done, when doing comparisons)
I have another zone which does play 5.1 natively, so I don't want to be creating even more duplicates in the library. I want to be able to send one file to either zone and have it play correctly.
This is also why DSP Preset tags don't work. I can't have a preset set to downmix 5.1 files a certain way, when those 5.1 files can also be played in a zone which shouldn't be downmixed.
I've gone over a lot of possible scenarios trying to figure out if there was a good way to get this sort of functionality without it, but I really don't see a good solution other than being able to group zones together so that they share a common playlist, having Zone Switch route the files from that playlist to the appropriate sub-zones.
What I envision would be similar to linked zones, except rather than having a shared playlist that plays to all sub-zones simultaneously, it switches between them.