Hi Petrty11. Although I've never heard your Rotel 951, from what I understand Rotel sources in general are on the dark side, and I think some might even say dull. I don't know if the addition of an outboard DAC would give you what you're looking for. If anything it would probably result in a more resolving presentation.
I do have experience with DH Labs T-14 Silversonic cabling, both interconnects and speaker cables and both proved to be much too lean and bright in my system. In my case, Analysis Plus Oval 9 speaker cables made a significant change in the direction you want. A much fuller and dimensional sound. I too own ProAc speakers, the Tablette 50 Signatures and they benefitted greatly from the cable change. ProAcs have a tendency to sound bright when the upstream signal is such. They won't mask it. On the other hand, there is also a sweet nature to ProAcs as well and I have found as others have that they really like tubes.
I started out with two different solid state integrateds similar to yours before finally settling on a tube preamp with a solid state amp. Now my system has both the warmth you're looking for AND detail along with a massive soundstage. I hate to misdirect you and add more confusion to the mix, but I really feel that you can do other things other than purchasing another piece of equipment.
If you do decide to go with an external DAC consider the Bel Canto DAC 1 which has a reputation for being on the warm side. I own the 1.1 which has a power supply upgrade, but the sound is very different, probably not the direction you want to go in. You can get a used DAC1 for about $500-550 on Audiogon. Let's hope others will have some good suggestions for you. Good luck!
