Dear Gerrym5: There is no doubt that your Lamm's are good tube design amplifiers aand that its quality performance is between the tube technology limitations that between other things means a high output impedance, depending on the " tap " the 2.1 goes from 1 Ohms to 2 Ohms that are considering high output impedances.
What happen with a high output amplifier impedance against the speaker electrical impedance is that exist anon-matched impedances and then the amplifier response instead to be flat fluctuate ( with differeces on SPL all over the speaker electrical impedance/frequency response ).
The response/what we are hearing in those conditions is a " equalization " on the signal due ( between other things ) to that un-matched impedances.
That " equalization "/deviations/colorations does not happen ( everything the same ) when the amplifier has a low output impedance ( say 0.1 Ohm ) and can match the speaker one.
Now, you like what you are hearing, you like those deviations/amplifier equalization, but that does not means is the best way to go with that speaker.
Just imagine your Lamm's with a low output impedance, that will be like " heaven " but unfortunately nothing is perfect and we have to choose the best trade-offs according our music-sound quality performance priorities.
Btw, Arwp the Krell Evolution could be well an " evolution " from what you own.
Regards and enjoy the music.
Raul.