I think it’s time for me to upgrade my audio interface. Right now I’m using an evo8 — 4 analogue inputs, 4 analogue outputs, bus-powered, and small enough to fit in a repurposed SM57 pouch.
However, I need more channels: I would like to have 6 analogue inputs (stereo monitor feed from FOH, my vocal mic, talkback mic from the bandleader, and stereo audio from one of my keyboards just in case GP crashes and I need to use hardware sounds) and 6 analogue outputs (stereo keys mix to FOH, vocal mic to FOH, stereo IEM mix, that’s five).
Small form factor and bus power are important because space in my luggage is very tight. And the ability to function standalone as a mixer is important in case the laptop crashes or hangs.
(Note: the only time my laptop required rebooting during a show was when there was a brief power interruption and my evo8, which was powered from my USB hub, freaked out and caused GP to crash. Restarting GP didn’t solve the problem so I had to restart Windows. After that episode I started connecting the evo8 directly to the laptop so hopefully this won’t happen anymore, but there’s always the risk of a USB cable jiggling loose so I want to have my bases covered.)
RME Babyface all the way if bus power is a must. RME UCX gives you the best capability/space ratio (8 ins/outs) but is not bus powered. I have one of each and they are both excellent for their purposes.
If these are out of your budget new, get the best used babyface you can afford. RME units last a long time. I had a 16 year old Fireface400 that was still working like a champ until I had to retire it when firewire fell out of favor. I don’t doubt it would have lasted much longer.
And I can’t vouch for MOTU gear. I had a MOTU midi interface that had terribly buggy midi. Hanging notes all over the place. I have much more trust in RME drivers.
I doubt that you’ll find a buss-powered interface that meets your I/O requirements.
The PreSonus Studio 1810c meets your I/O requirements. It has 4 combo mic/line inputs (2 also support instrument inputs for direct guitar/bass connection) plus 4 more line inputs, and 6 line outputs. It also has S/PDIF and ADAT connection support. It’s about as small as you’ll find in an interface that meets your I/O requirements.
I’ve been using mine for several years and have had zero problems with it.
The only interface I know that could possibly match your needs is the
Teenage Engineering TX-6.
It’s an ultra compact combined 12-IN 6-Out akku-powered usb-interface/field recorder/mixer everything.
It is very expensive (over a 1000€), extremely tiny (only 3,5mm connectors), and totally new designed.
If someone likes to experiment in a different direction than the “usual guys” go and give it a try.
I don’t know how this unit performs but I would stick to the other recommendations here:
take a solid and proven unit and do without usb power, take the external power connection.
I’m using a MOTU 828es (it is 19" so it is too big for your needs), the internal mixing possibilites are really great with MOTU interfaces.
The MOTU Ultralite AVB is a good choice. It has 8 analog outputs using 1/4" TRS. It has 2 Guitar inputs, 2 Microphone inputs and 6 1/4" TRS inputs as well. It has MIDI I/O and supports AVB networking which allows configuration/control via wireless. It does require 15VDC (provided) adapter to power the unit. This uses older USB 2.0 but I am sure it will connect directly to the USB-C with appropriate cable. No hub required.
Another option is the Focusrite Scarlett 8i6 which gives 8 inputs, 6 outputs and MIDI I/O and is lower cost $300 US. It also requires power via provided adapter. This interface has uses USB-C connector.
I use the MOTU interfaces which work well with Gig Performer. I am sure that the Focusrite interface will be equally as good.
I like my little Personus Audiobox Go. It sits on my digital piano, so I use it like a master volume for my Gig Performer plugins. (I still also use the sounds directly from my other keyboards, so they act as a sound sources and as controllers). Works for me.