Matching tube preamp to ss amp

pmm is correct

conrad johnson tube pre's for instance, have for years made their low output impedance an important selling point

cj premier 16ls2 is <700 ohms
cj et5 is 100 ohms

It is not be the best match, as others have said,  it is borderline. How low in the bass region do your speakers go? How do the pair sound to you? While saving for another amp. look into ones having input impedance of 50ohms or greater. 

I have not purchased the pre yet, it's about at the top of my budget right noa at $2K. Speakers are Qacoustics Concept 40 that are rated to go down to 53 hz 90 db sensitivity

There are a number of tube preamps  within your budget that have a lower output impedance. Jolida, Aric Audio, Quicksilver, Atma-Sphere, Van Alstine, Rogue, and others. 

Otherwise look for an amp with higher input impedance. Either way when changing amplification, I would improve on the impedance ratio.

Giving your speakers are not attempting the lower octave you may not be hearing a problem with your current matchup.

+1 @mesch .
For a modern preamp 2800 ohms is high.