If they claimed the mix engine has 48 inputs but it actually doesn't, they'd get returns for false advertising. Sometimes companies do some bait and switch with 'brochure speak' but they're not just flat out dishonest like that. The unit supports hardware expansion and the mix engine supports it.
You'd walk up to a live PA and rely on a feedback suppression plugin?! Brave man! (I get that you're not going to be using this live! Just sayin'
It's geared towards live use and that's why you'd want controls under your fingers in that scenario is all.)
Rolls makes a 6 channel headphone amp.
B-word makes an 8 channel one.
Look for a headphone amp with direct inputs for every channel. It turns out that SOP for these headphone amps is a single stereo input and they think you want that one input for all the connected headphones. Radio studio use or something I suppose. Some of them have an extra feature of direct inputs for every channel. Those are usually TRS dual unbalanced (like headphones).
You'll need to cable up appropriately. You may need to go balanced outs to unbalanced ins. (Not a big deal.) You may want to wire up the TRS inputs for multing a single line to both unbalanced channels. I think the B-word headphone amp has mono buttons and I think you can get away with plugging a TS mono plug into it and getting that to both ears with the mono button. Or wire up to patch two balanced outputs into a single TRS unbalanced plug for stereo.
Don't read that as 'issues' or anything. You just need to possibly mod a few cables a little. And then don't assume a headphone amp will have direct inputs per channel unless stated.
Story time just in case this offers any ideas:
I just set up my newly acquired X32 Rack.
Patched 6 channels of an 8 channel mic pre unit into the 6 balanced aux line inputs.
Patched the 7th channel into the talkback mic input.
Assigned the 16 mic input channels to mixer channels 1-16. (2 blocks of 8)
Left the default AES inputs assigned to mixer channels 17-32 (not using the AES inputs)...
But reassigned the 6 aux inputs to mixer channels 17 - 22.
(Because those channels are more featured with eq and 2 dynamics vs the default aux channels.)
XLR out 1-6 are for stage monitor channels.
TRS balanced aux outs 1-6 are for in-ear mixes. Patched to a Rolls headphone amp. (Multed for 6 mono channels like I mentioned doing above.)
The X32 has 16 mix buses available.
1-6 stage monitors.
7-12 in-ear monitors.
13-16 built in fx returns.
Then my extra wildcard feature:
If I don't need all those monitor mixes I can borrow a mix bus to route the talkback mic input to mixer channel 23. Using a mix bus was the only way to accomplish that connection.
So I have 23 Midas mic input channels and up to 12 monitor mixes. (Either 22/12 or 23/11 with having to use that mix bus for one or the other.)