Short version - I needed at least four additional line inputs for my Apollo Twin USB. I ended up with the Audient ASP880.
 
The results:
 
The  ASP880 sounds great! It is built like a tank. It does not use a wall wart or line lump (those things are unreliable for the most part). It worked perfectly at all four sample rates the first time, clocking off the Apollo Twin across the Lightpipe. It doesn't need a driver (yeah!!!). The switchable impedance is handy for some of my microphones. And I can bypass the microphone preamplifiers if I wish.
 
About as close to the perfect solution as I can imagine, and the only shortcoming - only 4 channels of S/MUX - is a "feature" of the Apollo Twin, no fault of the ASP880. And the price wasn't nearly as frightening as I expected.
 
The details:
 
I've been switching between a UAD Apollo Twin USB and a Presonus Audiobox 1818VSL for a long time now. Sometimes I even use WASAPI mode to combine them, but that doesn't work as well as one might like, so I switch depending on the task, and some days I'll limit myself to two microphones just to avoid the hassle of switching.
 
I finally grew tired of that drill, and went looking for an 8 input A/D converter that could send channels over LightPipe or S/MUX. There are quite a few, it turns out. Presonus makes/made a couple, Focusrite has a bunch, RME has a couple, as does MOTU, and used Apogee converters are nothing to sneeze at. There are others, but I can't remember any more names at the moment.
 
I didn't really want to pay for microphone preamplifiers, I have some good ones (Millennia Media, Melcor, TAB/Telefunken, SPL), and I like them. Other than that my requirements were sample rates up to 96k, S/MUX, and audio quality. probably not in that order.
 
Of the bunch I was able to scratch the Focusrite and Behringer immediately. They did not sound as good as the Apollo Twin, which was my benchmark. Of the remainder the Presonus and RME were the only ones that, while different, seemed like a good match.
 
And then someone suggested Audient. I've used Audient microphone preamplifiers, and even one of their consoles.They make good gear, but I was pretty sure it would be beyond my budget. So glad I tried them.
 
Audient has two current models - the 800 and 880. Both are 8 channel microphone preamplifiers with ADAT outputs. I could barely tell the difference in the audio quality, the measurements suggest that the the 880 is a tiny bit quieter, but I couldn't hear the difference. I do think the 880 handles transients a little better, but that could also be different instead of better.

The 880 does let me bypass the microphone preamplifiers and go straight to the A/D converter input. That works really well, and simplifies gain-staging. I have three preamplifiers hooked up the channels 3-8 now, and expect to leave it like that for a while.
 
I think I'd have been perfectly happy with the Presonus Digimax, at least for now. Spending twice that on the ASP880 was a difficult choice, but I'd like to think my ears, and my monitoring environment, will continue to improve.
 
Full Disclosure - I happened across an open box sale item, which saved me quite a bit. Since I didn't need any accessories that was just fine!
 
Bottom line - I am exceedingly happy with the purchase! No buyers remorse this time around!

Thanks for posting this. I have an Audient iD22, and was thinking of adding the ASP800 or 880. I think you helped make up my mind.

I happen to own two ASP800's. I got them because of the Retro Channel function.  It exists on the first two channels of the ASP800's 8 channels, and allow you to dial in some tube harmonic effects via a MOSFET circuit called 'HMX', and real transformer saturation effects via a dedicated transformer using the 'Iron' knob.  The other six channels are substantially similar to the ASP880's channels although the insert/bypass function is not there. 
 
I just wanted you to be sure that you were aware of the 800/880 product differentiation. 

GaryMedia
I happen to own two ASP800's. <snip>
 
I just wanted you to be sure that you were aware of the 800/880 product differentiation.

I was aware, in fact I tried the ASP800 as well. I didn't think much of the HMX and Iron features, they struck me as gimmicky. Don't get me wrong, they do exactly what they say, it just wasn't a feature I was looking for this time around. On top of that, the switchable input impedance was something I felt I could use, and it has worked well so far.
 
I also wanted to be able to bypass the gain stages when using other microphone preamplifiers. Part of the reason the HMX and Iron didn't appeal to me is that I have a couple "personalty" type preamplifiers already, as well as a nearly neutral one. The Melcor (predecessor to API) preamplifiers sound a LOT like an API, and have transformers, so I have all the iron I need. And my Tab/Telefunken preamplifiers provide yet another personality. I also have a pair of Groove Tubes preamplifiers when I want that particular effect.

If I didn't have those I'd probably be much more interested in the ASP800.

Got it. My reply was aimed at "Leadfoot" who was making up his mind.

Thanks Gary. I appreciate it! :)

I got an 880. It had noise as loud as the signal at the Nyquist frequency for double and quad rates. I had to ship it back several times before they successfully fixed it. Cost me around two hundred usd in shipping to get the firmware updated to a version that was not buggy.

In general, other than that, it has worked as expected. I use it probably weekly with the rme for extra inputs. I played a lot with the impedance switch but honestly I had a hard time hearing a difference once the tracks were normalized to the same loudness. I use what makes sense for the mics I'm using.

https://youtu.be/L3GKLkHxGqI

This video compares some sounds done with different impedence settings.