Condenser Mic with a Behringer Xenyx 802

Hi Folks

This is my first post here and I will keep it simple.

I have a Behringer Xenyx 803 mixing desk. I've used it with standard microphones connected with XLR connecters and they work sort of OK sound isn't that brilliant but OK. However a couple years back I bought a stereo condenser mic to record my father playing his piano. The mic needed a pre-amp so I bought a iMic which was fine until the iMic packed in.

I now have the 802 and tried plugging the mic into the XLR sockets and had no signal at all. So I switched on the phamtom supply and the LED's went overload but the signal then dropped to the point where there was no decent bass or anything just a tinny canned sound. I read in the manual that when I enable the phantom power I have to wait for system stabilisation, whatever that is.

Anyway when I switch off the phamtom thingy, the signal boosts until I get a really good sound, but then the signal dies out until there is nothing.

So, am I doing something wrong? I'm basically thinking that the condenser mic is too strong for the 802. But whatever is wrong, is there anyway of fixing this? I like the idea of using this mic because apart from the better recording quality, it is also small and easier to use.