Amps that don’t impersonate space heaters.

GanFet or Class A (sliding bias tech) SS amps

Class A done well has special qualities that seem to come at a price. Only tubes seem to extract a similar price, thermally. I can suggest a couple of options:

Combine a tube section preamp with a well-designed Class D (e.g., a ProJect Pre Box RS2 Digital and a NAD C298).

Use a modern GaN FET amp: Peachtree’s Carina GaN for example.

Use a hybrid amp with partial class A topology, NuPrime IDA-8 is compact and is a Class A- Class D hybrid which has been a successful model in that company’s lineup.

Your horns should do well with any of them.

@ghdprentice Thank you for the succinct description of high quality bass reproduction. I loved my slam back in my younger days, and noticed that it disappeared as I got into better gear, to be replaced by a more complete reproduction of the music. The nuance in the low frequencies is one of the best parts of a quality system. 

Seconding the Atma Class D's. Tube amps and A/B amps just roasted me in my hot and small upstairs bedroom. Atma's solved that issue with zero heat and they don't even get warm. I don't think I'll ever be selling them. 

I am most grateful for all of these intriguing responses. I am only familiar with Coda by name but I am obviously taken with many things spawned by Threshold. I didn’t see them at AXPONA but believe they have a presence in Chicago. Class D is also an intriguing idea. Again, I have scant personal experience but the dimensions and weight are most appealing to a person addicted to swapping out amplifiers and who will celebrate his 74th birthday soon. The fact that many suggestions accept balanced input a distinct plus as this is a cult I joined long ago. I wasn’t aware that Atmos-phere made a class D amp. Have always respected Ralph’s products. I have never owned one but OTL has always fascinated me since meeting ‘Gizmo’ at a CES in Chicago long, long ago. Again, appreciation to and for you all.