Tube preamp for Pass Labs x150.5 Amp

I currently have a AES AE-3 DJH Preamplifier linking together my Metrum Hex DAC and Pass Labs x150.5 Amp. The Pass is such a neutral/warm amp, that the AES tube preamp is making the total sound too warm in my opinion. I'm thinking of replacing the preamp with something not as warm, but would still like to stay with a tube pre. What would you recammend as a tube pre that could still have that tube sound, but not as warm? I'd like to keep it under 2K used or new, and am considering the Red wine isabella. thoughts?
Keep an eye out for a used VAC Standard preamp. Should be just what you are looking for in that price range.
Try ModWright preamps - they are certainly not warm and stereotypically tubey. Dodd preamps also. Both these manufacturers use 6H30s, which might represent the sound you're after.

Whatever you choose, using balanced outputs has always worked best IME with both the X150.5 and XA30.5.
I don't know much about 6H30s, I will look into it though. thanks
Atmasphere or Sonic Frontiers.
I have a Rogue 66 pre that I'm using with my Pass and so far, so good. Currently I'm using rca cables, and I'm on the hunt for a good tube preamp with balanced connectors. The Pass is absolutely one of my favorite amps so far...this year. I just obtained both in separate purchases recently, both used, and it's definitely the amp that has made the most significant difference for me. I'm keeping my Rogue Cronus Magnum integrated regardless, but the Pass is also a keeper.
If you are keen to introduce tubes in the preamp, I recommend: -

TRANSCENDENT Grounded Grid Preamp

You can buy it fully assembled from the master or really enjoy yourself and build it from kitset.
(Or perhaps even get your local tube guru to build it for you...)

Even fully loaded with the very best components that money will buy, including: -
A quality stepped attenuator
A quality switch
Additional RCAs if you need more inputs
Quality capacitors and resistors
NOS 12AU7 tubes
Teflon/Silver wiring
etc. etc. etc...

...I doubt you would spend more than $2k

This little amp is an absolute blinder, combining frequency extension at both ends (1 dB down from 5 Hz to 300 kHz!) with sizzling dynamics and that magic tube 'palpability' that we all love.

The web is full of reviews... Check it out.

PS: I built mine in 2002 and still keep trying new upgrades to see how much more I can squeeze out of it!
FWIW the 6SN7 is a better sounding tube than the 6H30 or similar tubes like the 6DJ8/6922. Frame grid triodes as these are not designed for audio and so while being very linear are also microphonic- and its hard to find one that is not.

The 6SN7 was designed for audio and so is easier to find a non-microphonic example, in addition they are quite linear too.
I have not heard an X-series Pass amp, but I'll vouch for the synergy of Atma-Sphere MP-1 preamp and XA-160.8 monoblocks. This combo is clean, neutral, and rich all at once.
try to find a used Pass X1
I just hooked up an Audio Research LS2 line stage to my X150.5 and I'm completely satisfied. Alas, my Rogue 66 Magnum preamp did not have balanced connections like the AR does, which I never experienced before. Still breaking in my Totem Hawks with this setup...