Problem with bi amping speakers


I tried to biamp my PSB Stratus Golds tonight using a Dussun V6i 150 watt SS integrated amp for the woofers and a Nobis Contigore 40 watt tube amp for the mids/highs. The contigore is similar to a Dynaco ST70. I used the preamp out on the Dussun and ran one cable to the preamp in on the Dussun and the other cable to the Nobis. Took the jumpers off the speakers and connected both amps to the respective terminals using the 8 ohm output on the Nobis.

When I turned on the amps, they both worked well for about a minute. Then I heard what sounded like feedback from a guitar amp, then ok, then feedback again, then the Dussun amp tripped. the Nobis kept playing. The feedback sound lasted for about 2 seconds each time.

Took it back apart, and both the Dussun and Nobis work fine alone. So what about my connections would cause this problem. I use a 2 male phono to a single female phono. One male end goes in the preamp out on the Dussun, the other male goes in the preamp in on the dussun, and an interconnect goes into the female end of the connector. There is one of these for each channel.

So, what am I doing wrong?
manitunc
Do you have one set of speaker cables going from the dussun to the bass module of your speakers and another set of speaker cables going from your nobis to the mid/hi module?
yes, one set from Dussun to low, one set from Nobis to mid/hi. I was playing a vinyl record on an Oracle Delphi V which has never had an issue with feedback, so I dont think that was the problem.
Is it like this?

Source>Dussun In>Speaker Cables>Low Module
Dussin Line Out>Nobis Amp In>Speaker Cables>High Module
yes, one set from Dussun to low, one set from Nobis to mid/hi. I was playing a vinyl record on an Oracle Delphi V which has never had an issue with feedback, so I dont think that was the problem.
Do your speakers instruction manual talk about bi-amp configurations? Not all speakers with dual binding posts and jumpers can be bi-amped only bi-wired. Don't try to bi-amp until you get more info from PSB.