Keith, I don't know if this was meant for me or Steve but over the years I have owned several ARC tube components (Ref 2, Ref2 SE, Ref5 SE) and currently own their top-of-the-line Ref 10 linestage and Ref Phono 10 (which btw is for sale at a v. attractive price.) The Ref10+RP10 as expected have excellent synergy not unlike Lamm pre and amps are synergistic.
I had the ARC 250SE monbolocks in my prior room for several months and included a comparison wih them in my
review of the
Lamm M1.2 Ref for TAB. I thought very highly of those specific ARC amps and still do (but bougt the Lamm.) There will be a time when I compare the M1.2 and
M2.2 hybrid amps - very interested in the M2.2.
I made a comparison between the ARC Ref Phono 10 and the
Lamm LP2.1 in my
review of the latter for PF.
I have copius notes on the the ARC RP10 compared with the in-house
Lamm LP1 Sig phono for its coming review, and also notes comparing the Ref10 linestage with the in-house
Lamm L2.1 Ref for its review. Those are next year.
Fwiw in 2009 writing for Soundstage I
compared the
Lamm LL2.1 Deluxe with the twice-the-price Atma-Sphere MP-1 Mk.III preamp when I owned the latter unit. That was my first encounter with Lamm electronics back when I still a newbie reviewer and knew nothing, but of course the review was spot-on.

Shameless tout that I am, there may be a surprise review in '22 that also talks about Lamm gear.
The Lamm Web site has a page listing many
review links organized by specific component. Many of those reviews include comparisons. I'm partial to Paul Bolin, Dick Olsher and a few others.