No separate "music" system for me. I simply run everything through a multichannel setup. Two-channel sources are played back through the two main speakers, while 5.1 material uses the full setup.

I've stated many times on this board that multichannel simply conveys a spatiality that I've never heard as accurately or as solidly rendered from a two-channel setup.

As an example, I've cited the SF Symphony's 5.1 SACD Mahler series. The two-channel tracks on those recordings sound great, and I can see how some listeners might prefer the two-channel mix to the 5.1 version. But, as someone who regularly sees the SF Symphony at Davies Symphony Hall (going there again tomorrow night for a concert with the Berlin Philharmonic), there's simply no question that the 5.1 mix brings the listener much closer to the actual live experience inside that particular room.

Also, with pop recordings, the surround speakers are used to create depth in the soundstage. While a good two-channel setup can also convey a sense of depth, that depth with the side imaging is much better anchored with a good 5.1 mix.

The problem with multichannel is that it requires much more optimization in the setup to fully realize the advantages. First off, you need the speakers to timbre match. Mismatching surrounds will only take you so far. You need a very close voice match in the surrounds to fully convey that 360 imaging.

Also, you need to make sure that the alignment and positioning are correct. The surrounds should directly face each other and position about 110 degrees off-center, and no more than 120 degrees. The height also needs to be optimized. About 1' above ear level is fine (though Dolby specifies at least 2' above ear level).

In addition, if the speakers are not all equidistant, then you need to adjust the processor to include a 1 ms delay for every foot of difference that the speakers are apart.

And then, there's the variability with the recordings themselves. As with two-channel, the listening experience with a 5.1 track greatly depends on how good a mix you have. In some cases (like Miles Davis' In A Silent Way and the Alice in Chains compilation), the multichannel mix is horribly done and the two-channel mix is much preferable. In other cases (like the Concord Jazz SACD series), the multichannel mixes remove much of the heavy handed processing used in the original stereo mix, resulting in a demonstrably cleaner sound and a clarity that was never heard in the two-channel version.

When all of these conditions line up, then you're talking about a listening experience in which 5.1 surpasses two-channel. As with all things in audio, YMMV depending on any number of different variables.