Thats kind of a curious range of interfaces??? Most are 4 chan then you have the MR816x?
I have the MR816x. You can pick them up for about $699 new (Sweetwater). While it has it's issues (most every piece of gear does), in terms of bang for the buck I'd say it's probably the best on your list.
The mic pre's are very clean, very nice sounding and have huge amounts of gain. Input 1 has high z capability so you can direct in a guitar or bass. The ad convertors are also very good. Dual headphone out's are a nice feature. an ADAT lite pipe in and out is very handy. SPDIF also and pretty good clocking and syncronization capabilities. A pretty nicely built unit, external power transformer is a little weird but works fine (not a wall wart...it also has a strange screw on connector that attaches to the unit itself. It is not a standard looking power cable).
Two modes of operation. If you run Cubase, it has an integrated mode that provides control of the unit from within the Cubase mixer itself. Works pretty well. Non Cubase mode uses a seperate piece of software that allows you to set up in's/out's, headphone mixes etc... Pretty functional.
Individual control of phantom power on each chan is a very handy thing (many units will groups chan's such that if you want phantom power on chan 4 you have to turn it on for chan 3 as well...or sometimes in banks of 4 chan's. That can get very cumbersome of you're using a mix of condenser and dynamic mic's.
In short, 8 chan's of nice mic pre's, good convertors etc for under $100 p/chan is a pretty good price/performance ratio.
The bad....while the drivers have been improved, they're not great. Not terrible but... The truth is, this is an area in which many of the all in one Firewire interfaces suffer. One person will get a box, hook it up and it works great. The next will get the same box, hook it up to what looks like the same kind of system and they have to fight their way through all nature of issues (high latency, random audio dropouts, clicks/pops etc...).
if you're going to run this on a machine with win 7 64 bit o/s, be sure to go into windows, select the firewire controller, and set it to use the "legacy" firewire driver. This is documented on the Steinberg site. The newer win 7 native driver will give you lot's of problems. It's essentially un-usable with major drop outs every few seconds. In all fairness, this is not so much a Steinberg issue. RME notes the problem for their Firewire interfaces as well (as do many other manufacturers). RME (as usual) has tweaked their stuff to work brilliantly with whatever windows driver you have but the Steinberg/Yamaha drivers are not that far ahead.
Having said that, once you set up to use the legacy driver, the MR816 run's pretty clean. It wont get latencies as low as the RME stuff (using the same asio buffer size) but its not bad. Use direct monitoring and it works pretty well.
Be aware, the marketing writeup says you can daisy chain several MR816's together, via firewire, and get up to 48 inputs. There is a gotcha here...The current driver will only allow you to do direct monitoring on the first unit. Steinberg has a tech note on their site that describes a way to get direct monitoring for all units but it's pretty convoluted and requiers you to have a version of Cubase that provides the "Control Room" feature. Not sure if the version of Cubase that ships with the MR816 (Cubase AI 4 or 5)has this feature.
Personally, I love the RME gear as my PC audio interface. Their stuff just works, reliably, trouble free, extremely low latency, but it's mighty pricey.
I needed more mic pre's, looked hard at numerous 8 chan mic pre's with converters but ended up getting the MR 816x. I attach it to my system using it's ADAT out's and connect it to my RME interface. Get's me the best of all worlds. Nice clean high gain mic pre's and a rock solid pc audio interface.
Hope this helps.
