I have 3 of the Dynaco amps, all rebuilt with computer grade caps, I like them a lot. If the amp is stock I would pass, if it's been gutted and rebuilt it's no longer a Dynaco amp and I would pass. With that said, I would opt for the Kenwood, I've also owned this amp, it's quite nice.
If wanting to later try a preamp and power amp then look for an integrated amp with pre outs, and main ins. This will allow you to later add a power amp utilizing the integrated as the preamp.
When looking to replace my long since sold KA7100 I decided this feature would be nice so opted instead for the similar powered KA7300. They look almost identical but that's where the similarities end. Notice the clean architectural layout of the true dual mono design, a definite homage to the legendary Supreme 600. This could possibly be your end game amp, it's that nice.
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With that said, you won't find one for the same kind of money as the 7100.