I built myself a media pc which I used for a while which had Blu-Ray/HD DVD read ability. I had all my CD's on it ripped to WMA Lossless and whilst the playback wasn't up to CD quality despite being a lossless codec, I listened to more music because of the ease of use. For example I've got a very large CD collection and it's very rare that I want to listen to a whole album, I like to pick and mix. With Windows Media Centre it's easy to have a party on-the-go creating on-the-fly playlists, I'd have been constantly up and down changing CD's which isn't good. The Blu-Ray playback will depend on your graphics card, I was using a nVidia 8600GTS silent card with no problems, however at the time I had it there was no HD audio pass through and playback software was a bit hit and miss.
I eventually ditched the media centre PC cos it was too noisy and too big and recently bought a TViX HD M-6500a media player (£299) + a Samsung 1TB hard drive (£75) to fit in it. I was expecting movie playback to be it's forte, but I've been presently surprised but it's music playback. At present it can't play WMA Lossless, so I converted all my music to FLAC and playback via HDMI to my Onkyo 905 amp. The sound is far better than from old Media PC which also passed a digital signal to my amp. I would go as far as to say it's easy as good as a decent budget CD player, having a fair bit of sparkle and deep bass. the major downside is that you can't create playlists on-the-fly as with the media PC. Having said that it's still more user friendly sitting on the sofa flicking through folders rather than getting up and down to change CD's. You can add M3U playlists, which is good, but hopefully on-the-fly playlists will come with a future firmware update.
With movies, the TViX can play almost all movie file formats including DVD ISO's, MKV and M2TS. Playback of DVD ISO's is superb, I set the TViX output to 576i and let my Onkyo upscale to 1080p. Unfortunately I've not been so impressed with HD playback via MKV or M2TS. With the latest firmware it'll pass through HD audio such as DTS HD which sounds fine, but picture quality at 1080p and 720p is very disappointing. There's a lot of noise on screen and it doesn't seem to out put a 24fps signal as it's supposed to. It gets nowhere near the original blu-ray images given by my Sony BDP-S350.
The TViX and most players of this sort appear to have their bugs! Constant firmware upgrades are required to fix old bugs and provide new features. However, each new firmware update seems to introduce a new problem! If you accept that you'll have to keep updating the firmware, these things are excellent, storing large amounts of media in a small portable box that you can take with you and plug in anywhere.