Preamp for Pass

George is right in fact experience has shown me the input impedance of the amp should be at least 10x higher than the output impedance of the preamp or the sound will not be right or all it could be.

Check the specs of your amp and search accordingly. Please let us know the specs of your amp and pre in terms of impedance. Very important.

I use an ARC SP-15 with a Pass Labs X350 and MIT cables throughout. This ARC preamp has a 200 ohm output impedance and the Pass 22 kohms input impedance. The ARC manual says 20 kohms min load recommended. Seems like a good match. From a listening perspective, I have loved this combo from the day I put the two together.

Can't see why the LS26 would have an impedance mismatch issue with the Pass amps, seems to be perfectly within the theoretical impedance considerations, as it has fairly low output impedance to a tube line stage (350ohm SE) - which does not mean it is an ideal match sonically, just that impedances should not be of significance in the pairing.

Atmasphere or Sonic Frontiers?

I had a Cary SP-05 Preamp with my Pass Labs X350.5. There definitely was an impedance mismatch with this combo. Very little bass and treble. Sold the Cary and bought the Pass XP-10.