We should be good to go. There's myself, Viper, Velomane, maybe acidbasement, maybe q2klepto, not sure who else. I don't know if Bear would come up on short notice; I'll shoot him a message.
I'm still waiting on the Oppo PM-1... it's supposed to be en-route so hopefully it gets here in the next day or so.
The RME Babyface has an output impedance of 30ohms... so unless you're using an external headphone amp, you're going to want a high impedance headphone and/or one with a relatively flat impedance curve. If going with Beyers, pick either the 250 or 600 ohm versions (I'd lean towards the 250 since the RME might not jave enough voltage swing for the 600 ohm versions).
I just noticed you're in Europe. See if you can find a Sennheiser HD25-13. It's a 600 ohm headphone but...
In a general sense yes, but the figure to look for is the sensitivity rating, which is generally expressed as dB/mW. The higher this number, the less power you need to get loud. Since power delivered is voltage^2/impedance, high impedance headphones need a higher voltage swing but less current to reach high power. Low impedance headphones on the other hand don't need much voltage swing from the amp but do draw a lot more current. Most amps fall somewhere lazily in the...
I haven't touched itunes in years specifically because of how limited my control was over my library. I switched to JRiver and while it has a higher learning curve, the full control it grants me is vastly superior. I'm unaware of what options are available for Mac however.
Unless you are completely married to the Apple ecosystem, I would highly recommend not using itunes to organize your music library. Save your metadata to the actual song files themselves with an external tagging program if you have to.