Are you doing your xo in the PEQ or convolution? If it's in the PEQ, the channel mixing has to be in the top PEQ box, and at the top of the list. If you do your eq before the channel mixing then the eq will only be applied to L & R. If you xo with convolution then the Convolver has to come before the PEQ or the same applies - eq will only get applied to L & R.
When you build filters in REW make sure the preferences is set to the same sample rate you have MC set for. I have MC resample everything to 48khz so I have REW set for the same. My mic pre is also set to 48khz. I've had bitdepth issues with MC and REW before as well. I have MC set for 24 bits so I build my filters in REW at 24 as well.
That said, yes, the sample rate of the file you are playing has to match the sample rate of the wav file you are using in the Convolver. MC recently has the ability to switch automatically to the right sample rate, but I think you have to create multiple wav files compiled at the different sample rates you wish to use. I like to resample everything to 48khz so it's a non-issue for me, and I have no idea how the sample rate switcher works in MC.
All that said, are you looking for an example of the config file I use in the Convolver or just a wav file?