Heard the same thing about the Altitude 16, analogue only. For a digital system it seems to be Altitude 32 and Datasat RS20i, both of which are limited to 16 channels when using the digital output. I think someone mentioned to me there's going to be a 32 channel digital upgrade coming for the Altitude 32 in 2018. Another option (have not heard it yet) seems to be the Storm Audio ISP, which already does up to 32 channels with digital output, but I think everything is downsampled to 48kHz. CBIV might also be an option but limited to 11.2 (?).
Again, not that I need the number of channels, but when investing a larger sum into equipment, it might be something to consider. They're all in a similar price range as the 861v8 and v8 is probably even more considering most of us went from v4 to v6 and then to v8. I've been out of the DIY audio electronics game for a couple of years, but I still wonder if a modern and cheaper processor like a Marantz or Arcam could be modified for a digital output. No idea what chips they're using these days and if it's even possible. But I guess that's really a discussion for another thread. Will do some digging and post if I find anything.