Wait, you want multiple nodes to be able to play into the distribution system? I think your big problem is going to be the software -- not sure how it handles being dynamically played into "collaboratively", I.E. the resource contention problem (you only ever want one person to be able to play into it at a time, neh?). Basically, the play device isn't going to matter, so you could probably get away with iPads, iTouches, laptops, ultrabooks, netbooks, etc.
Playback is entirely different and well-formed at this point -- Roku, Squeezebox, etc. all have plenty of such devices.