So if I understand correctly you're saying that I can choose to either have the PC or the reciever do the actual Dolby 5.1 decoding. And that having the PC do the dobly surround processing might be most convenient since I then I won't have to change any setting on the fly when switching between movies and music/games.
But that having the reciever do all the work might (maybe) produce better results - seems resonable and at least one of them should work well. And like you're saying; as long as it's all done in the digital domain on the PC and all the DAC conversion is done on the reciever it should give good results - I can subscribe to that theory.
Most of the time it is straightforward to assign whether the AC3/dolby digital and DTS codec (sometimes built into the media player or installed as a stand-alone codec depending on the software you are using to playback media) OR the receiver does the decoding. If you are a bit unsure of what you are doing, I suggest you start by using one media player to play all of your media (at least for stuff with a DD/DTS track) so you don't have to relearn how to do it for multiple programs. I personally use Media Player Classic Home Cinema mostly. In this program, you assign the whether the internal codec decodes these tracks by following the instructions listed in the second half of this blog post
. You can also use external codecs (such as LAV audio decoder). An external codec is one that you install separately from the media player program. The point of this is that, if you use multiple media players, you only need to set up once, instead of for each program.
In my experience, there shouldn't be any discernible difference in audio quality whether you let the PC codec, or codec in the receiver, handle this decoding. However, the initial result often sounds drastically different. I think this is mostly to do with equalization settings and similar level adjustments that the receiver automatically implements when being fed a direct DTS/DD signal instead of an already processed PCM signal. I know that on my receiver that the DTS tracks are louder by default and have more emphasis in the bass frequencies when I let the receiver do the processing. When you first hear it, you think "Wow! The receiver decoding sounds much better". But again, I'm skeptical. I think this is something that should be able to be adjusted via your receivers audio settings and that, with a bit of tinkering, for the most part, you should be able to get the sound to be pretty similar regardless of what is doing the decoding. But this could vary by receiver I suppose. And the reason for the discrepancy in levels is not always solely in the domain of the receiver either. Once you decode to PCM, your PC can then set levels. With the original bitstream fed to the receiver, your PC has no control over levels. This is why you can control the volume of multichannel PCM at your computer but ONLY with your receiver when outputing the original bitstream to your receiver.
Because the levels can be so different, at least by default, depending on whether feeding your receiver the original bitstream or processed PCM, and particularly if you have a room that is set up to give you accurate audio levels across the frequency range (ie, using Audyssey), it may be simpler in the end to just feed the receiver PCM at all times. If, however, you are convinced that your receiver just sounds better with the original bitstream, and you are OK with adjusting volume levels (and maybe even individual frequency levels) when you switch from PCM to bitstream, then by all means use bitstream. It's kind of something you just have to play around with a bit yourself I think.
But let me ask you this then: would you yourself go for an i5 with HD4000 graphics or do you think there are benefits to go with something like an i3 + GT640?
I was interested in the i5/HD4000 route for the sake of simplicity/minimalism but maybe there are driver/software benefits that come from using a discrete GPU?
Off the top of my head, I wouldn't think there would be significant (if any) perceptible difference benefit between an HD 2500, HD 4000 or discrete graphics cards regarding audio performance over HDMI. However, as I stated in my above disclaimer, other than a few brief stints with a laptop, I don't have any experience with outputting HDMI audio using Intel graphics chipsets.
If planning to do a bit of gaming, you may well be better served with something like an i3 with a discrete graphics card. However, I wouldn't recommend something less than, say, an AMD HD 7770 (and preferably an HD 7850) for gaming at 1080p: You can squeeze by with most modern 3D games (maybe not at the highest settings) gaming at 1080p with an HD 7770. You can't with a GT 640. Plus, the HD 7770
is only about $25 more than a GTX 640
going by Newegg. The only Nvidia part from their 6-series worth considering now is their GTX 660 - but that's a $200+ card...