Matching preamp out imp to amp in impedence?

I'm trying to narrow my search for a new preamp to go with my Pass X150.5. I would prefer to have some tubes in the pre. Upon reading the measurements pages of the Stereophile equpment reviews, it would seem that the Pass amp at 11K ohm unbalanced and 22K ohm balanced would result in a loss of low frequencies with the output impedance of the BAT 51se, the Herrons, the Aesthetix Calypso,the Hovland 100, and maybe more - I quit reading.
A bit of a problem is that not all of the preamp manufacturers (or other amp manufacturers) provide these specifications.
The Manley Shrimp has an output imp. of 70 ohms, that the reviewer suggests should "drive just about any amp".
I was setting my sights and budget higher - but I don't have the money to buy and sell a flock of mid to high priced pieces.
Can anyone help me make sense of this?
As a follow up:
Pass preamps put out 360 ohm balanced, 150 ohm unbalanced.
I'm looking for some tubes in my box, but I'm pretty sure the Pass preamps work well with their amps, so this should be some kind of reference.

I found a review of the CAT that said it put out 100 ohms,
and correct me if I'm wrong - that would be unbalanced.

Wyetech's upper offerings are 450 ohms or higher, except the coral @ 150 ohms.

What's it all about?