Blue Bear is right about ribbon mics needing lots of gain. Also, the Great River preamp would be a killer pre, and not just for a ribbon mic. However, the Midas Venice has alot of headroom. Gain wise, it should be plenty. I took my Royer 121 out on a live show the other day. On my Midas Verona I actually had to pad the premp. Of course this was also on a loud 100 watt Mesa Boogie stack.
If you can afford a Great River pre, you won't regret it. Personally, I had a client bring in one of those Oktava ribbon mics one day. I used it (along with another mic) because he had always "loved the way it sounded". I myself didn't like the way it sounded at all. There just seemed to be no clarity to it at all. I have a Royer 121 and absolutely love it on many different things, but especially electric guitars and certain acoustics. The problem here is that the royer is gonna cost about the same as 1 channel of Great river preamp, which is going to be a little over $1000. My gut says the Royer will sound much better with your Midas preamps than the Oktava will with a Great River. Then again, if you had the Great River you would have a really nice preamp for other things also. If it were me, I would make sure you got the best monitors you could possibly afford, then make sure you have a nice solid mic collection. Since the Midas pre's and EQ's are so nice, I wouldn't think too heavily about other preamps until after you get good monitors and mics. Once you do, I would seriously consider something like the Great River preamp. The Great river is a beautiful sounding, incredibly flexible preamp, and would be an excellent "first outboard preamp".