IMHO, and even without ever heard the MH stuff, I´d say you´ll notice an improvement in sound quality providing you already have great mics and preamps, and also good monitoring. But if your plan is to use the Rosetta as interface via Symphony or FW.... well: It works perfectly, but it`s a closed system. There´s no way you can add some other converters to the mix as you can do with the MH, because they don`t offer digital connections (yes they do, but then you can`t use the Apogee converters... so what`s the point?), and it doesn`t work with Aggregate Device neither. Because I had to sold the symphony system (loosing a nice bunch of $$$) and kept the Rosetta800 via ADAT to my RME FF800. Of course the Symphony system is somehow better, but I use lots of I/O and need something I can afford for non critical stuff, esp. when mixing... I record almost everything thru the Rosetta.
just my 2 cents