Some experiences with my two media players (not much info about formats, as I have given up trying anything that I am not sure they play):

The PixelMagic MB100 is only a player with optional internal HDD but no dvd player. It does not support Upnp. It supports Samba, but you can not specify a username/pw. This means that I can not see any media files on my Freecom FSG NAT server, so I only use a USB HDD.
I never know what the PixelMagic will play or not. I supports .ts streams, but often rejects Xvid or mpeg files, or plays them without sound. Flac is supposed to work, but the menu structure and playing options are such a hassle that I never play music on it.

The Kiss dp-600 is a dvd player with network support which can play media from a Upnp server like Twonky. However, both the dvd player and Upnp network support are very flakey so I also use a USB HDD with this machine.
I prefer the Kiss as it plays almost any tv-show that I download (mostly 800 MB files in Xvid 720p with AAC 5.1, or 400 MB files in Xvid 640 pixels wide with MP3 stereo sound). Also, it shows file names of any length that I have tried and the menu's and remote work quickly. Music options are very limited, no Flac or anything.

It would be nice to be able to play my Flac/Ape collection over a wireless network and for instance in random order from a number of different folders. This is impossible with the PixelMagic. The problem with my Kiss is that the connection to a Twonky server gets lost after a while and I have to reset the player, often several times, and reconnect. This can take half an hour.