Deep Exploration can open .ma and .mb Maya ascii and binary files respectively. Not mp though.
Ultimately, though, you are still going to get issues trying to work this way. Believe me...I did! Until I got the Max plugin working, I was trying to convert a model to cob format and then convert to pof using PCS. It was virtually impossible to preserve the correct hierarchy for any of the detailed stuff, and I kept crashing PCS with assorted geometry that it couldn't handle. It is designed to work with cob files made by Truespace, and geared specifically to the way that works. You might be better off downloading the free TS3.2 and just finding a file format Maya can export and Truespace import. Then you can set the thing up in Truespace and use PCS to convert.