Audio Research Preamp Experts?

I was an ARC dealer for many years and have personally owned almost every preamp/line stage that they have made.

My vintage favorites:

LS5MKIII
LS5MKII
LS2BMKII
SP9MKIII
SP9MKII
SP14
SP11MKII
SP6E

Are you going to buy an Audio Research amplifier? Some ARC preamps work better with certain amplifiers. The earlier tube units like the SP-8 MKII and SP-10 seem to work best with ARC tube amplifiers. I disagree with earlier posts. These older tube preamps have a very clean, neutral and low distortion sound quality when in proper working order with the right tubes and you won't know if it is working properly unless you send it back to ARC and have it checked out.

Next came the hybrids and they seem to work with a variety of amplifiers. I love the sound of an SP-11 MKII with a Levinson 23.5 amplifier. The SP-11 MKII also works well with ARC Classic Series amplifiers.

My favorite ARC preamps include:

SP-8 MKII
SP-10
SP-9 MKII & MKIII
SP-14
SP-11 MKII

If you don't leave these hybrid preamps on 24/7 you will never know what they have to offer because they change dramatically by day three. You won't think its the same preamp.

True that match to amp is a huge factor and very important to address up front.

Not just any SS amp will do. Same true of most tube pre-amps, not just ARC.

I would be using it with a Music Reference RM9 Special Edition. Over time, I have noticed great regard for the LS5 series. My understanding is that the LS5 is all balanced inputs and outputs, but my Merlin VSM BAM has simgled-ended outputs and the amp too is single ended - is this a problem? I am looking for bloom, 3-d, and expansive staging from the preamp. I've used the CAT SL1, Lamm LL2, and Joule LA150 Signature Edition. I use a Lightspeed Attenuator with the Music Reference amp in my set-up, but what to have a tube preamp under 3K to throw in every once in a while. I also want to own a "classic" that I can enjoy and admire from an early period.

Impedance matching between components from source through amp is the main technical spec that can be used to determine likely better matches producing better dynamics, lower distortion, etc..

10:1 ratio or higher of input impedance to output impedance upstream is generally considered good.

Tube gear like tube pre-amps has higher output impedances than SS making meeting this goal less guaranteed without checking first.

I suspect Merlin Bam to be tube friendly, so I would not expect a problem in general with tube pre-amps there, but BP would be the one to say for sure.