Why don't you do it the other way around? MPC into the U-5 input, then mic level out of the U-5 into the Neve pre-amp. Just a thought..

..Never mind...I just re-read your post and see this is what you ARE asking...!.. I think this will work, but you may have to make the cable to the U-5 unbalanced in it's input tho'.( I don't think the DI input is balanced). Are the outputs on the MPC, XLR or TRS? I think you will be fine going to the U-5 unbalanced scince you are making the signal mic level out of the U-5 into the Neve anyway!... Good luck..!