My system is BP25DA/4B SST/Watt Puupy 7s. I have had a Slimdevices player plugged into the BP25DA since the day I bought it three years ago. It is a wonderful setup -- so great, in fact, that I never even bothered to plug-in a CD transport.
There are a number of advantages to an SB3 over a mac mini. First, the SB3 has digital coax out, so no need to convert from optical. Second, the display and remote on the SB3 are very nice -- I like to be able to look up at my system and see the song information at a glance from across the room. Third, having the music server in another room is nice, as even the mac mini has a fan and a hard disk that are audible in quiet rooms (btw, the mac mini is an ideal Slimdevices server). Fourth, the Slimdevices community has created all kinds of plug-ins and add-ons that invariably prove to be useful (like mplayer for playing AAC Plus streams, or inguz audio for digital room correction, or iPeng, a Slimdevices remote for the iPhone/iTouch.)
Slimdevices also has 30-day money back trial period.
muski