The combination of the Raspberry Pi, RaspyFi, a TA2024 amp and for instance a Behringer UCA202 DAC with a set of small speakers just screams for a multi room setup that will be a heck of a lot cheaper than what Linn or B&O can offer. Might not be quite the same audio quality, but in many rooms where it is nice to hear the same music as in the living room, a high end setup is not feasible anyways, and a cheaper one will suffice.

But what do we want from a multi room setup? And how do we achieve it?

Let's set up an example, one that might be used in my house.

I have a living room with the main hifi from Linn. Here I have the RaspyFi feeding my Cambridge DacMagic, and I am quite pleased with the result so far.
In the kitchen I have a RaspyFi feeding a Sure TA2024 via a UCA202. Speakers are a pair of older Advent Mini. When adding to the system, I would like to have music in the office, the workshop, the guest room and in my daughter's room. For fun, maybe the bathroom and bedroom.

Having RaspyFi on each, controlling each from a client, with music files stored on a NAS, no problem, we just go ahead and do that. Much of the time music will only be playing in one room after all. There is a little problem, though, but that is with the clients. They are designed to handle only one MPD, changing to another one requires the changing of the IP in the settings. We need to modify a client to be able to hold information of multiple MPDs, and change between them at the touch of a button. I imagine that should not be a very big problem, but I may be mistaken on that one. There might even exist a client that can do this.

Pretending we have overcome the above task, how do we get multiple RaspyFis to play the same file, synchronised? I am thinking letting one RaspyFi stream the file and have the others in the group play that stream. Question is, can a RaspyFi handle both streaming and playing back locally at the same time? Otherwise we will have to set up a RaspyFi to handle streaming.

If a RaspyFi can handle both local playback and streaming, then we can create groups as we please. Select one as streaming unit and set the others to play back that stream. Creating another group is just repeating this, and in theory we can add as many groups as we have RaspyFis.The biggest issue could be the synchronisation of the music. It is important that music is played back at the same time in every room, otherwise we will get an echo-effect when we are in a location where we can hear two or more units playing back the same music.

If we need a RaspyFi to handle streaming, and not local playback, then we would need a streaming unit for each group we want to set up, but realistically, even in a large setup, how many groups would be needed at any one time? I would think that my requirements would be met by one streaming unit, if there is different music playing in other rooms, they would likely be for individual listeners anyway, and not shared over more rooms.

So, these are my initial thoughts. How much is actually needed to go into the MPD / RaspyFi, how much can be achieved by sending the appropriate commands from the MPD client?