Thanks. I will check everything. I have the feeling that the higher end consumer DACs are already tone adjusted for what they believe is the best average sound for most music and, as you said, the unaltered signal may be foreign to me. It may even be room correction. I have also read from other audiophile types that the flat sound is a bit thin compared to other DACs, so they may have experienced the same. With respect to equalizing, from what I understand there is no degradation of the signal, so other than a new perspective I probably should not too concerned. The reality is that once tone adjusted, it sounds fantastic.

Good call. I removed and replaced the cables and then did a factory reset for good measure. The sound was night and day. Not sure exactly what the problem was, but unit sounds excellent. I still do need to adjust the EQ to accommodate my particular listening sensitivities and environment, and choose wisely on the digital cable. My output options from my streaming server are Coax or Optical. Do you recommend either of these over the other when connected to the RME DAC?

Cool it works, yes it sounds very good.
The coax rca plug needs to good fit. It's important that the plug covers the rca jack completely. I don't think the coax cables themselves make a difference as long as it's a good one. I'm using Sommercable Vector, there are plenty of alternatives of course.
I've never used toslink and usually go for coax or USB, which is excellent with the ADI 2.