1.2k Output Impedance to 10k Input Impedance

I have a tube preamp with only single ended outs that does not have any output buffers and therefore a fairly high output impedance of 1.2k. My SS power amp has input impedances of 10k on RCA or 20k on XLR.

I have been advised by the designer of the preamp that anything lower than 50k or so will start loading down the line stage, so it would seem an imperfect pairing. My assumption is that at the very least I’d want to use the XLR inputs on the amp, as they present a 20k load to the preamp instead of the 10k vis the RCA inputs.

I have an RCA-XLR interconnect, but I’ve been told that simply using this will not result in a 20k load on the preamp and that the only way to accomplish this would be to use a passive transformer in line, such as the Jensen ISO-Max DM2-2RX.

For those that have experimented with these devices, do they result in any sonic degradation?

I'm wondering which might be the lesser evil – introducing an additional circuit and set of connections into the signal path via the DM2-2RX transformer, or running with a less than ideal impedance match between preamp and power amp. The answer is, of course, to try both and see, I'm just wondering if anyone has gone down this path before and what they found (heard).

Any inputs would be greatly appreciated.