well, i was in the exact same situation as you.
to make things short, i used to own the profire 610 and recently updated to the fireface 400...
i'm actually the user AGZ was mentioning in his comparison post.....and he's dead on. with the 610 you're fucked if you're trying to reamp, that's about it.
i'd say get the fireface BY FAR.
-way better converters: when i switched from the 610 to the fireface i was SHOCKED how much difference there was. the fireface is WAY cleaner, has more detail, better depth, stereo image, better resolution at the extreme low/highs....you know, people always praised the profire converters to be really a step up for m audio, and maybe that's true, but still they're way behind RME quality, that's for sure. this is D/A conversion mainly as it's easier to judge imho. i don't see why things would be different for the A/D side though
-routing matrix ROCKS. total mix is the perfect name....you get total control about everything. and it's friggin easy to do. the profire control panel was very limited in comparison
-preamps: here the difference isn't *that* apparent....i think the RME pres have an edge over the octane ones, but the difference isn't night and day really. both are very neutral and uncolored as someone already said, and imho the RME pres are even more so....which is a great thing imho, so all you need will be one (or more haha) colorful pre's for the mojo stuff, and for everything else or stuff that needs to be as true as possible just use the stock RME pres.
-obvious stuff....the 610 is very limited in terms of future upgrades....it only has spdif, no adat no nothing. the RME is pretty well equipped for pretty much everything you could throw at it. you could always connect better converters, more pre's and whatnot to the RME.....try that with the 610. for the 2626 it's different of course.....but there's one more advantage
-the RME clock is said to be REALLY good. this is also the reason why many higher level project studios tend to base their rig around the fireface....the total mix matrix, connectivity and the great clock just make it a breeze to do so.
so as you can see, i'm a big RME fan over here, haha. it was seriously the best money ever spent on studio gear, especially coming from the profire. luckily i still had money back warranty for the profire so i didn't lose anything
there are two not-so-great points though...
-be careful about your firewire chipset: ALWAYS use texas instrument ones! this holds true for pretty much every interface i've heared of though.
i bought the FF from a friend of mine who didn't get it to work properly, and the VIA firewire chipset turned out to be the culprit. but once again, this isn't RME specific at all....just a word of caution.
-at times i found the (WDM?) drivers of the RME to be a bit dodgy....e.g. when i'm running reaper and try to reference some stuff using winamp, i'm sometimes getting error messages as reaper is still blocking the drivers....for some reason i didn't experience this with the profire. i'm not saying that this is a biggie or something, but i felt that i had to mention it to be fair to the poor profire lol.
basically you only have to make sure that reaper or whatever is in offline mode, otherwise it's blocking the drivers. if you've done so it's running smooth as silk though.
overall the RME drivers are said to be REALLY stable though, and so far i can confirm this in the sense that i've never had any reliablity issues as of right now.
regarding the monitor thing, yes it's WAY easier to use if you have a monitor controller....but then again, they're not that expensive, and using one is always a good idea imho.there's just something about having a real analog level control that's independent of what the software is doing...plus you get to use aux ins, several monitor pairs and whatnot....i use the sm audio pro whatever it's called, was like around 120euro or something iirc...
anyways, hope this helps some....if you got any more questions, just ask
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