The EQ is fantastic, especially when coupled with room measurements. To that end, I have a Umik-1. The EQ helps me address the room nodes and generally smoothen out the frequency response. The effect is palpable and better than no EQ applied to my ears.
Insofar as the default bass and treble settings are concerned, with them set at 0db (or EQ off), my system is tuned for listening between 80db and 90db. When the decibels drop any lower or higher, it helps me get the desired bass and treble those volumes (read fletcher munson curve).
This depends upon the frequency response and sound signature of your current speakers.
the default shelfing frequency for treble on the RME is 7.5khz. if your speakers already have a prominent top end, increasing treble will increase its impact and negatively affect the balance of sound perceived by your ears. Try and couple bass and treble with room measurements to reap maximum results if the default presets do not suffice. The RME has incredible flexibility in that regard allowing you to target exact frequencies instead of relegating users to predefined curves.