Hello,
I've just taken the plunge and bought a BDP2 from HiFi Lounge in the UK.
Details:
Serial # 347
S1.75 2014-05-01
Build: Loony Loon (RELEASE)
MPD: 0.17.3
Kernel: 2.6.32-5-486
Copyright Bryston Ltd. 2010
The sound quality is amazing. 
I have tried upgrading to MM and end up with problems and have to return to Loony Loon (I take an image copy of the CF card before the upgrade).
I am using the firmware20140430.bin to perform the upgrade with an empty thumb drive in the front USB.
(http://dl.dropboxusercontent.com/u/86196657/firmware/20140526mm/filesystem.new etc.)
The first phase completes and the system reboots. The front panel eventually says "Restarting....." but doesn't restart. You can no longer ping the BDP but the front panel buttons continue to work. After leaving it for about 1 hour, I pressed the front panel power button. The display says Powering down and shows a countdown timer, 5, 4, 3, 2, 1 and powers down.
Upon powering up, the upgrade continues. Each time it has to shutdown or reboot, the same problem - No network - can't ping, but the front panel is still active. Use the front panel power button, countdown timer and off.
Eventually, the upgrade completed with the repartition and MM running. The poweroff/reboot problems continue - It won't shutdown or reboot EXCEPT from the front panel and every time a countdown timer is shown. When it is in this half shutdown state, there is no network but you can still select and play from locally attached media - so MPD is still running (?).
I have then used MM for a couple of hours with mixed results - however, I returned to Loony Loon so that I can just chill out and listen to the music 
Thanks,
David
I've experienced this same problem. After four hours of a rough (at best) effort to upgrade to MM (it literally just worked one time, where it hadn't several times before), I now have several bugs....
=BDP will not shut down via the software (IR remote or hard button only)
=BDP initially had no MPD running, and nothing I did would get it to run at startup. I eventually switched to 18.6 and was able to get it to run.
=There is someone elses play list when I start it up... 13 songs, none of which I own. Sometimes, I can clear the playlist, sometimes I can't.
=Similar problem in artist view. Sometimes, it stays and I can see Arcade Fire and others. Sometimes, it blinks away.
=When the playlist is clear (in default view), adding a song doesn't add it at all to the left panel play list. But it DOES add songs and they show up if I click the play list icon.
=I tried a factory reset to clear any extraneous data. Now, the "Bryston BDP-2 Player — Stopped" display flickers on and off (about 5 times a second or so) under default view. It stops when I click on a song, but it happens again if I leave and return to the default view.
=Memory is up at 97.3%?! Is that used? What's causing that? There's nothing playing, no playlists loaded, and no operation (that I can see) going on. CPU is idling at 9.6% and swap is 0%. I'm ONLY running SAMBA, USB Mount, and MPD.
=My playlists are gone, but there's one called "top40" that I never created?
=I just clicked that "top40" play list, and now all I CAN see are someone elses songs. I can't even see my music at all anymore. (a reboot fixed being able to access my internal SSD, but the rogue playlist still persists).
The image below shows the playlist that came with the new firmware. I have none of those songs. And nothing I do will allow me to add my own songs to that list.
OS is Windows 7 Pro (all updates), Chrome (updated), BPD has a fixed IP address and is accessed via ip address, connected via ethernet to a switch, then to a router.

This feels a lot like beta software. I'd really like to go back to LL so I can just enjoy my BPD. Is there any easy way to do that?