*DAC

I have a modified R26 with external 10MHz clock and prefer the Weiss DAC204 with the stock power supply. I hear a small improvement by swapping the stock power supply with a linear power supply.

With that said, I find the R26 to be a good value and great for the DIY hobbyist given all the modification opportunities.

Huge R26 Thread

Based on what you are looking for, I believe that you will like the Weiss DAC204. This review compares it to a more expensive, currently well regarded DAC.

Weiss DAC204 Review

@navyachts the suggestion by @ghdprentice to try a Chord DAC is right on target I think. Chord has a great tone, good dynamics and offers few filter options to fine tune the sound. I was running a Chord Qutest when I had the Martin Logan Montis with Pass XA30.8 Class A amp and it was a very good match. 

Also, just my opinion…the Martin Logan 13A are warm and delicate sounding speakers when it comes to the presentation. Your amps are Class A and that in general is going to mellow things out all on its own with sweeter treble and plush bass.
So just some options aside from changing a DAC…look into trying different speaker cables and interconnects. I can’t tell what you’re using now but if the cables are contributing to additional warmth in the presentation, you might still be facing the same challenge with a new dac. Again, just a thought…

Ah…just went back to your system page and saw this

Stock power cables, Blue Jean speaker cables (12 awg - 6ft long) Blue Jean interconnects 

is that still accurate?

IMHO (from personal experience) the cable or power cord/vibration devices can be the issue. The good news is they are a lot cheaper to address. After spending $170 for a 1.5M Pangea coax (same specs as DH Labs @ $240) I tripped across a thread here about Ali-Express Chinese cables. I have no issues saving money especially on cables. Dipped my toe in the water and ordered Nordost Odin 2 (name knock-off), both a 1.0 and 1.5m for half the price of the Pangea! Figured it would sell quick but noooo. Anyway, the Odin 2 brought my entire system to new levels of enjoyment. After sufficient break in with the 1.5 I swapped it out for the 1.0m and was further shocked that a mere half meter shorter could reveal so much more. I wound up replacing all the cables in my system, but moved to Odin 2 Gold which gives me more texture, aka fuzz on the peach.

Since I swapped out the Odin 2 for Odin 2 Gold for over a year I have been searching for a Odin 2 Gold coax cable which I finally found and should be here in a couple days: price a mere $46 dollars and free shipping

HTH