I'm a strict believer in separate units.
If you're looking for AES/EBU Digital in, you're not looking for an amp, you're looking for a DAC. To meet multiple outputs requirement from this DAC, you can simply use a splitter.
For multiple headphone outputs (while taking single or multiple input while maintaining separate volume controls for each headphone): essentially, this is multiple amps, some just have a few amps in one box. I think you will get much better performance and bang/buck by simply going with multiple amp units.
To that regard, grab a nice DAC with AES/EBU input, run the output through a splitter and use multiple amps. This will be a very modular system and you will get the best performance out of it.