It's looking more and more like a DIY USB 2.0 solution might be the way to go, with the added benefit of being able to extend it beyond 24/192 should the need arise. S/PDIF is only specified to 24/192 and thus off the shelf receivers are not available for anything higher, but something like (differential) I2S over CAT5 might work out quite well.
BTW, some exotic audio hardware can do as high as 32/384. While that's unlikely to provide any benefit over 24/192 for ordinary audio applications, I suppose it could come in handy for DIY sonar and SDR applications.