Tube Preamp/ McCormack Amp impedance matching

Whether it is optimum or not is ultimately determined by your ears, your expectations, and your speakers (not listed). I agree it sounds like an adequate match on paper but there is much we do not know.

I would forego the pursuit of impedence matching devices and wait until you have done a lot of serious listening to the basic set up with your speakers. If it ain't optimum to you then consider if the sound's inadequacy is caused by an impedence mis-match or something else. It could be corrected by something as simple as a tube selection in the pre-amp (isn't that why we like tube amps/pre-amps? :-), and not need impedence matching devices to get you where you want to go.

FWIW

Foster 9, To add to your burden - some pre-amps with 2 outputs have them configured so that both outputs cannot be used at the same time to drive two different amps at the same time. I have a pre-amp configured as such and when you add a 2d system you load down the other output and change the impedence relationship.

I have another pre-amp with two outputs which will correctly drive 2 amps etc at the same time with out loading each other down. With the former, I compensate by using one set of outputs and using a Y connector splitting the signal between the two amps. If you are experiencing a roll off when you are driving two amps, etc, off two outputs, check with the pre-amp manufacturer to see how the outputs are configured, don't make an assumpion that something that you can fix is a problem.

While I agree with Bob's comments, this falls under the "but there is other information we do not know", I wouldn't be overly concerned with the actual impedence curve unless you are trying to solve a problem. I have a pre-amp with 600 ohm output which sounds fine with an amp with 10K input even though the manufacturer recommends 20K, and conversely I have a pre-amp with a 3500ohm output which doesn't interface well even though the amp has a 47K input. "On paper" they both should be fine but the mismatch (or lack of a mismatch) shows up on listening. Also, SS amp output impedence curves matching speaker impedence curves are not usually a problem for a high quality SS amp unless you are driving a substantial sub 4ohm load at certain frequencies in the speaker, a problem usually solved by getting amps with high current (and possibly power out put as well depending on the speakers efficiency) and the concurrent ability to drive 2 ohm loads.

FWIW.