Hi
The Raven gain is about 13.9 dB (5X voltage gain). The RCA and XLR inputs have the same gain. The Khozmo volume control has a very nice log taper and you should have good adjustability in most systems. Not touchy.
I would run XLR from DAC to Raven if you can, but it is not required. It will generally sound better with most DACs. Also, if you ever change amplifiers you can run XLR out to an amp with balanced connections. The RCA output of the Raven will by definition have less gain. That said, there is plenty of gain to drive almost any amplifier. I believe Spatial has a return policy if it doesn't work in your system, but honestly, it will work well with most anything, single ended or balanced.