The impedance tailoring device(s) I mentioned are described on this old A'Gon thread (as well as a TNT write up on one).
https://forum.audiogon.com/discussions/autoformers-the-benefits-in-matching-amp-to-speakerhttps://www.tnt-audio.com/accessories/zero_autoformer_e.htmlNot certain if they would apply to the 5A/Lamm combo, but perhaps Ralph from Atmosphere can chime in.
I've only listened to the 5's (not 5A's) with 100wpc ARC tube amps (Randy @ Optimal Enchantment) and noted that the main speakers ran very low on their own as the powered subs rarely kicked in with a variety of source material.
They were fine with the ARC's in Randy's fairly large listening room (super high ceiling) even @ uncomfortable (to me) SPL's.
The speakers were placed @ least 6' out from the front wall, so little room reinforcement there.
We were going to try them with larger (200wpc?) ARC's, but there was a cabling snafu that voided it.
I preferred the warmer sound of a BAT CD deck and preamp VS an all ARC setup (ARC preamp, CD deck and amp).
An Oracle/SME TT source sounded nice with the all ARC setup though.
DeKay