Tube Rolling Advice for the Backert Labs Rhumba Extreme?

Tomorrow I have a Backert Labs Rhumba Extreme 1.2 being delivered, which has been upgraded by Backert to 1.3 specs. It will be driving the Luxman MQ-88uSE and the front end is a Qutest with M Scaler (Innuos Zen MK III server/streamer). Speakers are La Scala IIs, placed about 15' apart in the corners at a 45º angle. Soundstage is excellent and expansive with remarkable placement of instruments across the sound field.

If all goes well it will be replacing my L-509X, which is currently only being used as a preamp for the MQ-88uSE, so it’s being underserved in my system and will need to find a better home.

I am interested in any advice about tube rolling with the Backert Labs pres. With the Chord digital front end, I am getting a very layered, dimensional, detailed sound and thanks to the Qutest filters I’m able to adjust filters to best match the amplification. The MQ-88uSE has a gorgeous, full, warm sound and right now the 509X’s solid state pre is giving a nice sharp, detailed, and dynamic profile to sharpen up the tube sound a bit.

I don’t want a syrupy or bloated tube sound, more airy and detailed on the top with holographic imaging with solid heft on the bottom end. I’ve replaced the preamp tube in my Cronos Magnum II with a Cifte and was really happy with the impact on the sound.

The Backert comes stock with new Mullards, which I expect may have a slightly warmer sound than what I’m chasing.

Any advice?

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NOS medical grade Amperex from Brent Jesse.Not cheap but wonderful sounding.
@milpai that is interesting to hear, thanks for the follow up. I did remove the o rings on my Cifte’s for a couple of days and I could not really detect a difference to be honest. I do have mine on a slab of wood that is also sitting on 3 IsoAcoustic Oreas, so that combined with the terracones on the unit itself may make it less susceptible to noise? Or the Mazda Cifte could be less microphonic than the Gold Lions. I replaced the o rings and have left everything as-is.
A little over a month in and it is still sounding amazing with the MQ-88uSE. I did replace both power cords on the Rhumba Extreme and MQ-88uSE with Transparent High Performance PCs and I have noticed an improvement in detail, which I attribute to a lower noise floor overall in the system. 
I’m currently awaiting the Hugo TT2 to replace my Chord Qutest DAC; along with the M Scaler, I believe the Hugo TT2 will likely be end-game on the system. I couldn’t justify the expense of the DAVE and I have read rave reviews of the TT2/M Scaler combo (together surpassing the sound of the standalone $12K DAVE).
Recently changed to a Psvane 12AU7 and love this tube over the Gold Lions. These are much more open, slightly less warm, but tons of details and superbly balanced. I got mine from Viva tubes in MA.

My dealer tells me that using tube adapters and 12SN7’s sound better than 12AU7’s. Has anyone tried this?

My regular Rhumba 1.3 came with the new-production Mullards.  I got some new-production Genelex Gold Lions from Jim McShane which I liked a little better.  Then some older Blackburn Mullards from Brent Jessee which honestly didn't really seem to improve on the Gold Lions.  But now I have some fancy Amperex 7316's installed, and they are the best yet.  Can't imagine rolling again any time soon.  Full rich, sound.  I would have tried the new-production Psvanes, but Amperex is giving me everything I look for.