I've been thinking about this same thing lately. I use a Behringer XR18 in my band's rehearsal space as a live mixer and the thing is really nice (somewhat surprisingly given the brand). It has a full blown 18-in/18-out USB interface with ASIO drivers. I haven't quite stressed the USB in the same way as with a studio interface but I've used it for recording rehearsals, virtual soundchecks, etc. and it has been flawless so far (usually using Waves Tracks Live). I also played around a little with using it with SONAR as a live VST host running an electric guitar direct into the mixer then USB into a SONAR track with TH3 on it and then back out over USB to the mixer channel. That worked flawlessly as well and with decently low latency. 
 
The downside for the XR18 is that the preamps, etc. are "budget" quality. However, they have a Midas branded version of the box -- the MR18 -- that has upgraded Midas pro quality preamps, etc.. I suspect it would make a pretty nice studio interface. 
 

I'm not really a Presonus fanboy. I have to say this though. I think they have the best integrated mixer/interface setup for the medium to larger studio to date.
 
At the bottom of their line is this. It has a built in sd card recorder and bluetooth PLUS a multi channel usb interface. It goes up from there to motorized faders scene recall and plugin sharing with SO3. 
 
Bottom of the line
 
Moving further up the line

Dave76
The downside for the XR18 is that the preamps, etc. are "budget" quality. However, they have a Midas branded version of the box -- the MR18 -- that has upgraded Midas pro quality preamps, etc.. I suspect it would make a pretty nice studio interface. 

I have the XR-18 and the Preamps are "Midas Designed".  They sound nice.  I do wish I would have waited for the Midas branded one, but I had my XR18 a full year before it shipped.  This is my first dance with a digital mixer and the routing takes a while to wrap your head around.
 
I had the Mackie 1640 before that (The one with 16 channels firewire).  I got $400.00 for mine.  Guess I got a good deal.  It was $1500.00 new (sigh).
 

batsbrew
adat IS probably still the best choice.
 
mixers are limited typically, 
otherwise everyone in the world would use them,
and apparently they don't

I think the major issues with home recording using mixer/interfaces is the scale of requirements. If just two or three people are concurrently recording, then a typical 8-channel interface and some work within the DAW to handle headphone mixes is fine.  When there's a 5 or 6 person band, especially when there's a drummer, then a mixer really shines as a better approach to realtime monitoring for headphone mixes, metronome distribution, and managing multiple playback speaker pairs. 
 
The cost point for ever-higher input channel counts and a nice set of effects in a mixer has now solidly stepped into the range of traditional interfaces.  I write this from the high channel count perspective of using a Midas M32 for my interface.  As I read the OP's requirements, the first product that made sense to me for his requirements is the Midas MR18.  
 
If you're happy with software-based controls, as you would generally be using with a traditional interface, then there's plenty of function and quality to be had in the MR18, and you're not paying for a built-in display screen and motorized faders. 
 
I read though some other posts in this thread (too lazy to build a second/specific response) and would like to point out that the additional latency through an ADAT preamp into an interface is typically in the range of 15 to 50 samples depending on the product.  To cite some specific examples, I had been using the ADAT output of one of my Audient ASP800's and tech support confirmed that the XMOS had 2-samples of delay, and the PCM4204 chip had 37-samples for a total of 39.  My ART TubeOpto 8 has 32-samples delay in A-to-D function, and 22-samples delay in D-to-A.  With that data you can convert to specific values of fractions of a millisecond depending on your sample rate. 
 
As for whether the Behringer preamps are 'budget' preamps, it's a fact that the quality of Behringer's new products hasn't been able to fully insulate them from shame of some of its long-ago sins in the audio world.  My website shows some specific test results that compare a few performance aspects of the X32 preamps to the M32 preamps.  Overall, the essential message is that you can make a good recording with the X32 preamps as represented across their newer (XR18, etc) product line.  I admit that part of my decision to move from the X32 to the M32 included the weighting factor of the brand-sensitivity of my clients.  Nevertheless I regularly encounter X32 products in live venue situations, and I'm absolutely happy to use them because I know that I can get good recorded results. 
 
As I wrap this up (my oatmeal is getting cold) let the record show (ha ha) that I've also done both live and studio recordings with the PreSonus mixer/interfaces.  If I was choosing a mixer/interface today, the short list (in alphabetical order) would include the Behringer, Midas, PreSonus, and Soundcraft product lines.
 
Enjoy the process.
 
 
 
 

I would agree with you Gary on the older stuff. The X32 is still a strong contender. The new Presonus Series 3 you may not have tried. Both are great.
 
I see it this way. Many here on the forum buy both an audio interface and a tactile software controller. Then they proceed to integrate everything into their setup. 
An alternate plan would be to buy it all in one unit and have the added luxury of software made for it. This is why I'm considering that option.

By "budget", I'm just pointing out the fact that the major price differentiating factor for the X Air series versus the M Air series is the quality of the preamps as well as ADDA converters. Beyond that, they are pretty close to identical units with different branding. I don't have experience with the MR18 but my understanding is that you get a noticeably lower noise floor versus the XR18 which would be of benefit for the studio. I believe the same applies for the X32/M32 series but those product lines diverge a bit more in some other ways. I'm more than happy with the XR18 and its preamps/converters for my purposes. I just can't vouch for how that translates over to the studio.

GaryMedia
I think the major issues with home recording using mixer/interfaces is the scale of requirements. If just two or three people are concurrently recording, then a typical 8-channel interface and some work within the DAW to handle headphone mixes is fine.  When there's a 5 or 6 person band, especially when there's a drummer, then a mixer really shines as a better approach to realtime monitoring for headphone mixes, metronome distribution, and managing multiple playback speaker pairs.  
 

In my case, the requirements boil down to permanently setting up recording chains with the least hassle for the best quality, for a broke a** musician working solo.   Live drums, electric guitar, acoustic guitar, bass, vocals and eventually cello.  I want it set up, ready to record when I feel like it, any instrument, at any time.  
 
The least hassle means *not* playing with ADAT expansion interfaces.  I really wish that could work, but I can't seem to find any information on how latency is handled with two devices with different processing times.  I've scoured the web for articles, and they get really close, but they never really touch on the point I'm after.  So, I gave up asking and researching and said "f**k it, I'll buy a mixer with at least 16 mic pre inputs and be done with it".  
 

GaryMedia
If I was choosing a mixer/interface today, the short list (in alphabetical order) would include the Behringer, Midas, PreSonus, and Soundcraft product lines.

 
I do really like that MR18 you mentioned.  Not sure if the Soundcraft compares in quality or not, but for a couple hundred more I can get hardware control of the board, which I'd really prefer if I'm going to have a mixer.  I can see me inventing new cuss words working with a wireless tablet control solution...
 
 
 
 

I recently started to use a Behringer X-32 and it works fine as an audio card so long as you don't need more than 44.1 kHz. The mic pres are Midas so no problems there.

Voda La Void
 
In my case, the requirements boil down to permanently setting up recording chains with the least hassle for the best quality, for a broke a** musician working solo.   Live drums, electric guitar, acoustic guitar, bass, vocals and eventually cello.  I want it set up, ready to record when I feel like it, any instrument, at any time.  
 

Do you need multiple inputs for that? I play guitar synth so I have both a mixer and sub-mixer. I have various synths and guitar synths going into my mixer. Since I'm only recording myself I don't need multiple inputs - I just have 4 inputs in my audio IF and the mixer goes into that (and a line in from a guitar amp). Everything is setup - I just move faders on the mixer up and down depending on what synth or processor I want to record. 

I highly recommend the Soundcraft MTK series.

I will write more when I get to my computer. This phone is a nightmare.