A couple of issues back I reviewed Tascam's Trackpack 2x2 which includes the US-2x2 audio interface. I concluded that it's a good package to get a home studio started, but sometimes you just need more. In the case of the Celesonic US-20x20 you get quite a lot more.
The US-20x20 has 20 channels of IO - that's eight 56dB, high headroom mic pre-amps, two line inputs and up to 10 digital IO channels on S/PDIF and ADAT. It uses USB 3 (or 2) and has AKM Audio4pro converters for sample rates to 192kHz. It's worth noting that the IO count falls to 16 at double sample-rates (88.2 or 96 kHz), and to 12 at quad-rates (176.4 and 192 kHz) as always happens with ADAT.
On the back panel are the USB, digital, MIDI, BNC Wordclock, line-in and 10x line out sockets, plus the DC input for the wall-wart power supply (with a lightweight retaining clip) and an Auto-Powersave switch. More clues about what you can do appear on the front panel, with a power switch (thank you) followed by a Mode button to select Mic Pre, Audio Interface or Mixer modes. Past that are the eight mic inputs on combi-sockets with hi-z instrument options on channels 1 & 2 and line options on 3-8, bank-selectable phantom power (1-4 and 5-8 - it would have been nice to have a little more control over this), individual gain controls for the mic pres with basic signal present/clip LEDs, line-out 1-2 level control (for your monitors) and two headphone sockets with independent level controls.
I reckon you can figure-out most of the functions by just reading the labels on the panel, but there's a 44 page Reference Manual and 104 page Owner's Manual online if you need some additional help (in four languages to be fair).
Ergonomics are good; the unit ships with the same type of angled end panels that I liked for desktop use on the smaller interface and the box also contains a set of brackets for rack-mounting. Once you've got your digital and MIDI gear plugged in and patched your dedicated line IO as needed, everything you need to access is where it belongs on the front panel. Except for the bits that are controlled by software. OK, download and install (took about a minute). Drivers are class-compliant by the way.
The unit was recognized on my Windows10 machine immediately. The software recognizes the current mode of the device and gives you the appropriate options. In Mic Pre mode the analogue inputs are connected to the analogue and digital outputs and as you'd expect, so stand alone operation is simple and uncluttered. Mixer mode allows a surprising amount of control over the built-in 6-bus DSP mixer, complete with gain, eq, compression and reverb, and Audio Interface mode additionally lets you choose how to route your IO into and from your computer. The mixer screens may take a few minutes to get used-to, but it's really all pretty straight forward once you get orientated, and when you get the set-up as you want it you can save it as a scene.
In use - certainly you'll find more esoteric pres and converters with perhaps a little finer detail, but these are good quality, clean and quiet just as they need to be (and if you have access to those top-end pres you can always patch them in using the line inputs or digital connectors). Operation was both things that it needs to be: simple and reliable. Reviewers are pretty well conditioned to complain that input metering is too basic, but really, turn it up till it clips (if it does - these pres have good headroom) then back the level off and it's fine - beyond that use the level meters on your recorder.
Pricing is such that it's realistic for a project studio - if you can afford enough mics to need an eight mic input then you can probably afford one of these to plug them into. The digital IO (and let's not forget MIDI) gives a lot of flexibility, the USB3 connectivity is probably the most future-proof option available at the moment, and with a laptop you can even use it as a mixer for your band. Oh, and Tascam includes the USB3 cable! Overall it's good quality, well priced and very flexible; I can see these units getting a lot of use in studios and mobile racks.