For me having different combos is too expensive, so I am looking for kind of nirvana to be the best suit for my 325is. So far, i have highly modded Beresford Caiman DAC sourced from my MBP/Audirvana gear and I liked it witm my 80i's. With 325is I don't know yet.
In your case, the combos are mostly vacuum tubed, does it mean that I should take a plunge into it, because Grado like tubes? I have listen recently to jazz, some classics and old rock.
For the amp I have Marantz PM6004 and would be nice to keep it as well as CD5004 player. Both have rather poor headphone amps comparing to the Caiman DAC.
I'm surprised the Marantz PM6004/CD5004 don't sound good!
The Caiman is only a DAC, correct? After briefly reading some reviews, its supposed to be a nice DAC
Also why haven't you tried the 325's with your set up, or is it that your not sure if you like the 325's with this set up?
Out of all of my current amplifiers, only the LD1+ has tubes, but it is a hybrid, it also has an OP-AMP, and it only costs about $115.00U.S., so it is a very nice inexpensive amp, and you can roll the tubes to your sound preference and also change the OP-AMP. And yes I think it sound great with the 325's, but I also did some tube rolling (6J1P-EV Voskhod tubes $15.00U.S. shipped) and changed the OP-AMP to a Burr-Brown OPA-2107 ($7.34U.S. shipped), and all in all I like the sound with all of my headphones through the LD. BTW, sounds like you have some nice equipment also, I'm surprised the headphone outs don't sound good.
If you are interested in the LD1+, I would definitely recommend it! Also matched with the Caiman, you should really enjoy the sound out of them together.