For low impedance loudspeakers there is only one tube power amp I would suggest: the Music Reference RM-200 Mk.2. The amp was designed specifically for low impedance loads, a job at which it excels. Do a Google search and read all about it. Reviewed by Michael Fremer in Stereophile (in both original and Mk.2 iterations), residing in the mag’s Recommended Components list Class A Tube Amp category for many years.
I don’t know what you mean by "vintage", but the RM-200 was introduced in 1998, the Mk.2 version a little over a decade later. It typically sells used (of course) for around $3000, a real bargain. I’ve owned ARC, Atma-Sphere, and Music Reference tube power amps, and have settled on MR for my remaining years. They’re all great, but for low impedance loads the RM-200 is the one to go with. IMO, of course.
Power output is 100 watts, and from just a single pair of KT88 or 6550 tubes per channel! The Atma-Sphere M-60, in contrast, uses 8 output tubes (16 for a stereo pair) to produce only 60 watts, and is not well suited to low impedance loads.
$3000 is 50% more than your $2000 budget, but $2000 is unfortunately just not doable. Save up, or sell something else!
