gja - There are a few things I would recommend to make sure you're getting the best possible performance from the de capos (and the rest of your system) before making a decision:
1) Definitely replace your cables. Given the amount of money you have invested in your front-end (and now in your amp as well) your cables are IMO probably a significant weak point. With a TNT 5 HR, you have a front-end source that offers more resolution and music than most will ever see from their digital source--you should definitely experiment with cables that are in the same class.
From my own experience, I can recommend Van den Hul. The Integration Hybrid could be a good match, and The Second is an excellent cable in
specific applications. I would avoid The Seconds for now because it is difficult to match; but in the right system it can be an incredible cable. A good match for speaker cables would be the D-352 Hybrid (I'm using these now, bi-wired) or, if you want to move further up the line (which I would encourage you to try), the Magnum Hybrid or the Inspiration Hybrid. The De Capos are wired with Van den Hul internally, so Tash often recommends and demos with Van den Hul. (Divergent also distributes the line.) As I have mentioned
elsewhere in this thread, moving from Kimber to VdH made a huge difference in the musicality and coherence of my system.
I have also had fabulous results with Acoustic Zen interconnects, brainchild of respected cable designer Robert Lee (formerly of Harmonic Tech). The Matrix Reference is a great cable; and can be found used. I have also heard wonderful things about their speaker cables (the Satori), although I haven't tried them (yet).
There are lots of other great cables out there--these are just the ones I have experience with. If you have a dealer you have worked with, try a whole line at home (two interconnects and a set of speaker cables) that are roughly at the price point where you want to be in the near term (not necessarily what you can currently afford out-of-pocket). If you have audio buddies with a range of cables, so much the better.
There is also the matter of bi-wiring.
Contentious, to say the least. See the other thread. At the very least, I encourage you to replace the foil jumpers that come with the De Capos with a jumper made of a quality cable. Whether or not there is a benefit to bi-wiring (with two runs of cable) is an open issue, but I would advise to at least try 'shotgunned' cable so that you have two sets of leads at the speaker end.
2) Experiment with speaker position and height. The de capo's bass response will vary significantly with distance from the back wall [I've just gone through a compelling example: I moved the speakers back toward the wall for a party last night (to avoid any unfortunate bumps or wine spills), and several times I went back to turn off the subwoofer only to find that it wasn't on.] Staging will also improve based on speaker position.
Speaker height also has its own
thread here. I would try experimenting with books or something, just to make sure you have the right height.
3) Your amp switches between 4- and 8-ohm output, and also has a Triode/Ultralinear switch. Experimenting with all the combinations will be essential to get the best performance; of course the results may vary with repertoire (triode for vocals, etc.). I would take a look at Dan Davis'
review in TAS if you haven't yet.
I can't find any information on your current speakers. What can you tell us about them? What are you trying to improve with this change? If you have dedicated servo amps, I'm guessing that the sound is very controlled--it will be interesting to see if you get the same sense of control from the Rocket/De Capo combination. Also, depending on how much bass your current speakers produce, you may want to think about adding a sub later? We should have a thread about that, too...