New to Preamp - Preamp suggestion around 10k

That sounds like an unusual arrangement for a Stax amp. Bypass its internal preamp with an external one? There is no such preamp stage in most direct-drive Stax amps, which need to supply 50 - 60 dB net gain (more similar to phono stage, minus the EQ). I guess you could bypass the volume control, or perhaps you’re dealing with a design that puts traditional pre & power amp stages before some output step-up transformers to supply the needed gain.

Anyways, you can’t go wrong with the ARC Reference 6 or 6SE. They’re fantastic. Or a VAC Signature (used) if you want more midrange sweetness. I’ve tested both (well, a VAC Master in my case) feeding headphone amps, and yep they sound great. I also had an RP-9, and it has a leaner midrange with less sweetness than the ARC and VAC. Though I did also try the RP-9 feeding a headphone amp, and it can indeed work well too - nice punchy bass. The Ref 6 and VAC have a lower noise floor than RP-9. There are reasons they cost more.

Also, quite honestly I prefer Rogue’s older Athena and Hera models over the 9, but I understand I’m a bit of an oddball ;)

I currently have a VAC Master, ARC Ref 6, and VAC Renaissance III in my stable and I STILL hang onto an Athena because I just like it and it’s so good for the money (I regretted selling my Hera). It's dirt cheap compared to these other preamps, when it does pop up for sale.

Question for the group.  The OP is looking for "slight bit of warmth, plus better dynamics and imaging" and is asking for pre-amp suggestions to help with that.  Is a pre-amp the right tool to solve this issue?  Or would looking at different headphones make more sense?  

It (somewhat) depends who you ask. This approach is not without precedence. The traditional "problem" with Stax headphones specifically, compared to dynamics and planars, has been lack of warmth (on some models, like 009) and weight in bass. There's a guy who was using a high-end tube preamp into a $14K Eksonic T2 (direct drive electrostatic amp) to try and "flesh out" the sound. But after reporting initial success, I'm not sure he stuck with that setup. Another example: the Woo 3ES is reportedly a fancy 300B preamp stage bolted in before an Apex op-amp based direct drive circuit. The implication being that the 300B stage in this case is not really necessary; it's there to color the sound in a pleasing manner. 

In my somewhat limited experience on the matter of pre-amping a headphone amp - you can move the needle a bit in the intended direction with a preamp, but indeed I would lean to the camp that one should keep searching to choose a headphone + amp combo that is more attuned to your preferences, rather than try to add another preamp upstream. I found my "match" with a different T2 build (different HV transistors makes a HUGE difference, more than rolling the tubes in these amps) and Stax 009 headphones :) 

@cming0038 @bdp24

So far I’ve only owned the MC SUT’s by EAR (absolutely fantastic SUT’s), but I’ve long been curious about their other tube electronics. Especially their preamps and HP-4 headphone amp. I bet they’re fantastic. If I were to pick another brand to try on a whim, EAR would be atop my list, then Manley :)

Interesting, I didn’t realize the T-8000 had that feature. Must be a volume control bypass intended for DAC’s with a digital control. What you’re trying to achieve here seems reasonable!

Also - don’t know how you feel about "Stax Mafia" / Kevin Gilmore electrostatic amp designs, but you might consider snagging a KGST (cheaper), KGGG (more expensive), or BHSE (Headamp, more expensive) when they come up on the used market. Just avoid any Chinese builds and stick to known builders.

Even the T-8000 is reportedly significantly underpowered compared to the Gilmore designs. I admittedly listen pretty loud, and have heard the Stax 727 absolutely fall apart, to mush, as I raised volume. You won’t get good dynamics and solid imaging if it’s going that way, and a more powerful amp would have a much bigger impact than adding the preamp in that case. The Mafia’s all-solid-state deigns (KGSShv, Carbon) can be a bit on the leaner and brighter side, which I definitely don’t prefer, but their tube hybrid designs really pull it together for my tastes.

In particular I find the KGST a nice pairing with L700 and 009 without breaking the bank.

• KGST - Kevin Gilmore Single Triode, using 6S4A tubes. It's the simplest amp in this lineup.
• KGGG - Kevin Gilmore Grounded Grid (EL34 driven with grounded grid)
• KGSShv - Kevin Gilmore Solid State, High Voltage version
• Carbon - Modified & improved KGSShv with Silicon Carbide FET output transistors
• BHSE - Blue Hawaii was Kevin’s first attempt to replicate Stax’s legendary T2 amplifier before he had access to its circuit diagram. Her scribbled out this design on a cocktail napkin while drinking Blue Hawaii’s on vacation lol. The "SE" indicates Headamp’s (Justin Wilson) improved and modified version.

@cming0038 Nice! If you’re happy with the resultant sound, that is what matters.

Having a reference system (or systems) and comparing gear over time will develop your ability to quickly pick out a specific component’s sonic disposition (warm & sweet or dry and analytical etc).

For me, the RP-9 was not warm nor sweet compared to the ARC Ref 6 or VAC Master or VAC Renaissance III (or even the older Rogue Athena and Hera). However, I did like its bass punchiness, and overall clarity & detail. To be fair, I may never have burned it in "fully". But the VAC's were sweet from hour #1 lol. Maybe Rogue should do some initial burn-in and auditioning like VAC does (if a VAC component doesn't make the cut in audition, it goes back to the line). 

Your post is making think I should experiment more along these lines -- since I have a few nice preamps, headphone amps, and headphones at my disposal :)