I've used TopoR with DXP, and they work together very smoothly. Please have a look at
**broken link removed** There is a tutorial answering your question.
TopoR imiports and exports data in PCAD ASCII format. As soon as both PCAD and P*otel belong to @ltium, P*otel DXP can import and export PCBs in PCAD ASCII format as well. There is a warning message "unexpected end of file" when DXP imports the routed PCB back from TopoR, but apparently it does not affect anything.
BTW, TopoR was quite amazing, and I guess you won't regret using it. It is fast, and it does not use scripts, so it is easy to use. Routing results looks a bit unusial, but the number of vias and total track length are definitely much less than I've ever seen from other autorouters.
I found that limitation of 125 nets in the TopoR Lite (freeware version) is very generous, it is well above my current needs.
I am just wondering, are you gouing to run P*otel and TopoR under Linux, as your nick suggests?
Please let us know if you manage to do it, it would be rather interesting.