Impedance Mismatch ???

Could be.

I would probably not be concerned with most any amp input impedance 10K or higher for use with SS mainly. Use of higher output impedance tube pre-amps is the scenario that is more problematic. Tube pre-amps are popular with audiophiles these days but are probably still a very niche market overall. Many amps including stock Icepower have only 10K input impedance. That may just be the most practical approach with the most appeal.

I love the sound of my ARC tube pre but I am sure there are similarly good sounding SS pre-amps out there for reasonable cost as well. My next pre-amp I buy and keep someday will likely be SS as long as it is not a step backwards from teh ARC.

I say that because even my 30+ year old SS NAD 7020 receiver that I am using in my family room system today as a pre-amp only with the TAD Hibachi amps and OHM 100S3 speakers sounds very good, although it is guilty of a touch of that warmer sound that NAD can be known for. Its' my long time spare unit that I put it in to replace my similar older Carver pre-amp in that system when the Carver developed a problem needing repair. I would like to try a newer good quality SS pre-amp in there sometime soon when I can come up with a good justification at which time I might try a shootout for my ARC pre-amps place in my main system.

Larryi, that might be the case but when he designs whole amp (instead of using Icepower modules) most likely he has option of setting 10k or 40k input impedance without extra stage. It might be electrical noise issue since higher impedance input is more likely to pickup interference. Preamp side is low output impedance, but not at the radio frequencies where it might be tens of kiloohms. It is tradeoff between performance of the best amp and convenience of matching for lower end amps. It is feasible that, as you suggested, he targeted class D amps for use with tube preamps while his new model 625 is class AB.

It would be a good question to ask Jeff Rowland. I'd be interested in the answer.

There are always tradeoff issues in designs. I'm sure Rowland know what his are for each particular product.

usually impedance is measured at 1000Hz signal that may show different values.

There are certain amps, such as the Krell Cast stuff that have the preamp acting as a current source, rather than a voltage source:

http://www.krellonline.com/cast.html

If this is the case, preamp output impedance and amp input impedance must be exactly the same. But this is a very unusual circumstance.

For most hi-fi rigs I actually look for a minimum ratio of 20:1.