I want to chime in and sing a bit of praise and bit of criticism of the Motu Ultralite AVB.
At first: There’s someone who began the work for a fader control of the internal Motu Mixer: https://github.com/Silhm/motu-mcu-control , but I haven’t really tried it.
In general I’m quite happy with the Ultralite AVB, the sound is very fine. I actually prefer it over the RME sound, it’s a bit more musical, yet precise, but I’d take this with a grain of salt, comparisons of sound without ABX-blind testing are quite subjective and error-prone.
The big advantage of the AVB models over let’s say the Ultralite Mk4 is the ethernet port so that you can connect an iPad (via a small router/access point) for controlling the mixer directly without any host-computer. You don’t need a special and expensive AVB-switch as long as you don’t want to use other AVB equipment.
The Touch Console is really nice to use, I’m looking forward to use it in connection with a Behringer ADA8200 for more inputs via ADAT in a live context, standalone.
Also the Ultralite AVB works fine via a Camera Connection Kit with an iPhone and I’m planning to use it with a powerbank for field-work.
The negative points are in my experience:
It doesn’t really work nicely with Linux, I always got crackling or it took ages to connect, depending on the firmware version, some worked better, some were unusable, but none worked really good.
And the internal reverb FX doesn’t sound really good to me, but a good workaround for standalone mode together with an iPad would be to use a good reverb plugin on the tablet, maybe with AUM.
The drivers and therefore the latency and stability of RME are still unparalleled in my opinion. The Ultralite AVB works fine and totally usable with my Windows 10 computer, but my RME Digiface achieves better latency. But i heard, that the Motus shine more on Macs, but haven’t tried it personally.
Having said that, and in recursing to the thread starters original question:
I still use an analog mixer (Soundcraft FX16 II) in front of the interface as a kind of patchbay in my small studio.
Soundwise, using the internal Motu mixer is even better and one can work more precisely with fully parametric EQs and Gates/Comps on every channel, but I find it more convenient and first of all more inspiring to use the analog mixer.
For example: I want to just play/rehearse on my Rhodes, I just turn on the Mixer, dial in some bump in the upper mids and a bit of reverb and start to play without having to wait for boot times or worrying about certain settings or even recording at all.
I’m also fond of dub-like production, using the whole studio as an instrument, and there it’s good to have everything laid out nicely in front of you.
I also totally can recommend a mixer with a sub group: I got my interface hooked up on the subgroup, so with a physical switch of a button I can route something to be recorded to the DAW, where a new track is by default getting the input from the Group/ Channel 1/2 of the Interface.
Regarding Modular-levels: Both the Soundcraft FX16 and the Motu happily take a direct output from the Modular, without a dedicated output-module.