Is no preamp really better that a good preamp?

I guess my final question, then, is what kinds of specs should I look for in a preamp if I want to add one at some point?

"What gives"
My opinion.
Don't like it? Move on.
Good luck with your selection.

But you haven't offered a single helpful comment to my questions or to any of the other responses! What kind of "opinion" offering is that?

09-26-15: Rustler
I guess my final question, then, is what kinds of specs should I look for in a preamp if I want to add one at some point?

As I've said in some past threads, the main usefulness of specs, IMO, is to allow candidates to be ruled OUT from consideration, based on poor or questionable technical compatibility with the other components in the system, or on the basis of user preferences such as cost, size, weight, appearance, remote control capability, etc.

In this case I believe you are fortunate in that from a technical standpoint it appears that your existing system would be compatible with the vast majority of both tube and solid state preamps. The one slight question mark that occurs to me involves some preamps, such as certain Conrad Johnson models, which provide very high gain (e.g., 25 db or more). Gains in that vicinity, or higher, MIGHT cause you to have to operate the preamp's volume control undesirably close to the bottom of its range if (as would presumably be desirable) the preamp were used with the volume control on the DAC set at or close to the top of its range.

Beyond that, all I can suggest is that you research what kinds of preamps others have reported to provide good sonic results with the same or similar speakers and amplifier. "Similar" meaning, at least, Martin Logan speakers and high powered class D amplifiers.

Good luck. Regards,
-- Al

09-26-15: Rustler
I guess my final question, then, is what kinds of specs should I look for in a preamp if I want to add one at some point?

Ah!! now that's another ball game, if you want to colour the sound in some way instead what you get going direct, this will be a bit of a merry go round, as all preamps have different sound signatures, and no one here could give you the right answer to which to get unless they are you.

Cheers George