I owned two KA-5700s, and loved them. dug the cool little meters.
Also owned two 7100s. Loved the recessed, sunken bezel.
I'd personally go for a bit more power over the base 5700, say the 6100- and retain the meters.
I'd also go for the sexy 7100 with that great design of the sunken recessed center knob, over the slightly more powerful 8100.
The 9100 is a sweet amp, but difficulties scoring parts for it would steer me away. Even though there's supposedly bypassing techniques and fix-arounds.
I also owned a 5500, 6500 and 7500 tuner. Size-wise, the smaller tuners fit well with the vintage gear. But that 7500 tuner was a killer performer.
I had the wood cases for a few of them. Didn't really like them. I've seen the wood sideburns and like them better, as well as the nicely designed rack handles.