RME ADI-2 direct to amp

OP I don't own this dac yet but I'm researching it.

Sometimes the Dac designers when they offer Dsp (volume control and such) on the Dac  will account for not losing resolution and the RME is a well designed dac. I think you would like to stay at -6 to -3, to avoid possible clipping and not too low -10 and more allowing the extra headroom to increase possible noise floor. Maybe read the manual since I heard it is very complete.
Did you purchased the pro model? You are biamping and I also read the pro model with dual chips have independent channels for 2 possible amps, one balanced one single ended, I am biamping (planning triamping too) and thought you might be interested.

In regards to the preamp question I have tried dac direct with a project S2 and Denafrips Terminator in my system using hqplayer Dsp (with Denafrips) as volume control and I preferred a preamp (preamps) over it, the choice of going direct I think it is very dac dependent (on its output), it seems the RME benefits this design but I am not completely sure since I haven't tried it.Some others have used analog stepped attenuators controls (gold point) with dacs to avoid the preamps and digital Dsp and preferred this too but it is a gray area some experts say the attenuators have their own tradeoffs and well designed digital Dsp (especially when you are already upsampling like me with hqplayer) are better. I choose to believe these are, if it is real or imagined I have no idea, it sounds good enough to me and the math behind it makes sense.

@luisma31,
I do not have the Pro Model. I am using an XLR splitter cable to the 4 channel amp, then using the RCA outputs to a sub. 

Really loving the EQ ! I have a small bump at 120 and 500 for a little punch increase. I hear no negative effects from this. While not exactly cheap I believe the combo of functionality and sound quality make it tough to beat. When I finally go back in the office I may take it in for headphone listening.  

So some of this RME manual is over my head! The amp I just started using does not have a gain control. At normal daytime listening levels I am at around -50 on the digital volume control of the RME direct to amp. Am I losing bits like this? I thought I read somewhere you can change the max output voltage of the RME to compensate for higher power amps. I can't find this in the manual? Anyone know if this is true or I just made it up? It also has relays click off and on in the RME for certain volume ranges. Is this used to not lose bits?

Hi

Go into the line out menu in section 19.1.   The menu's hierarchy is described in detail in sec 12.     Specifically  Line Output Reference level.   If you set it to " - 5 dB " this should help to get the volume above -30.  

Also try Auto Reference Level.   That setting uses relays to change the out put in the analog domain, using less " digital" volume.   You can hear the relays click as you go up and down the volume scale when engaged 

That setting may work better, try both...