I have an older Kenwood TS-690S that does the same thing... It automatically kicks in a 20 dB attenuator between 500 and 1700 kHz. Plays fine, sounds good with an external speaker, makes for a pretty good all-around SWL / BCB radio.
When I first got it I wondered how much better it would be at BCB DX'ing without the attenuator. Then, over time, I came to realize my DX'ing wasn't limited by sensitivity but by noise and co-channel interference. 20 dB of more noise and three-stations-at-the-same-time isn't going to pull anything out of the soup. Years ago there was a program on WLS that I enjoyed. 890 kHz is shared by WLS, a Spanish language religious station in Laredo, TX and Radio Havana. Some nights I could hear all three in sequence, some nights I'd hear all three simultaneously. Sensitivity / selectivity was not the problem...
BTW: Last time I looked, the only BCB station that still has a truly clear channel is KDKA in Pittsburgh, PA @ 1020 kHz. Some nights it isn't there at all but the noise is running S-5 or better. Nothing to be gained by more gain.
