I am triamping and Pure Music has a built in crossover that works seamlessly with the RME. Crossover points and slopes are adjustable along with polarity and gain. Very flexible. You can add whatever plugins you want if you want EQ or whatever. I play around Fab Filter ProQ for EQ.
I did it myself. The transformers are 1:1 that Dave wound specifically for this purpose. If you contact him he can give you a quote. http://www.intactaudio.com/index.html
Probabaly around $200 each so you'll have as much or more in transformers as you do the RME. There are cheaper transformer options but Dave's are very, very good.
The tricky part is you are soldering on surface mount components which is very easy to mess up, and of course you void your warranty. I bought a used RME on eBay.
The RME has 8 channels of audio output with 4 stereo DAC chips. The chips have balanced outputs which are cap coupled to opamps. The mod bypasses the opamps by soldering the transformer primary directly to the outputs of the chip. Hook whatever connectors you need to the secondary running balanced or single ended as needed.
The traces are teeny tiny so very easy to burn up a trace which I did. Fortunately I only need 6 of the 8 channels so I'm still good to go.
I am an electronic tech but really no experience or expertise in dealing with SMT soldering. If you find a repair shop that is they should be able to do the work for you.
The RME sounds very good stock so you could start there, or explore other pro audio interfaces; Apogee, Lynx, and many others. Bear in mind the RME is Firewire and some others are USB.