I accidently tested whether a Powermate 2x and 4x would work together the other night after I'd captured my Jupiter-ISS near-transit.
I left the 2x on by mistake and added the 4x.
The result was a 300 pixel diameter image of Jupiter (along with Callisto and Europa) that wasn't too bad quality - not up there with some of the amazing images I've been seeing here but ok for a little telescope.