You could get a meter and check for DC leakage from the preamp before connecting it to the amp. You should only need the coupling capacitors if there is any leakage.
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You probably should ask Krell some of these questions. Generally, I had no problem when I used my Krell KSA 80 (the smaller stablemate of the 200) with an Audio Research SP11 Mk II hybrid preamp. As far as maintenance, you could get the serial number and ask Krell if the unit's been back for repairs, as I think they keep that sort of information. I would also recommend sending the unit to Krell for them to go over it, if you do buy it--they would replace the caps, which I understand they recommend at this point given the unit's age and should run in the $4-500 range, if I recall, but the nice thing about high-end companies such as Krell is that often they'll replace other, smaller items for little or no charge while they're performing their contracted repairs.
When I was a Krell dealer in the 80s I often used a hybrid preamp with KMA 100 and KSA 100 and others of that era. Given a properly designed and operating preamp it is hard to see any trouble. Krell's reluctance to recommend tube units apparently stemmed from the DC leakage problem mentioned earlier.