Kdvditters

I need to be able to merge two or three different bass clef staves, into just one stave. I am trying to create piano versions of concertos, symphonies, etc. and am using the voices from the basso continuo instruments as the bass clef, (violas, cellos and double bass), but when I import the midi, (and just the selected voices), afterwards I am unable to merge together the two or three staves that represent the left hand chords on a piano. They always come in separately, and I don't want to manually enter thousands of notes on the bass clef, (from the 2 or 3 sets of staves), to make the chords. Thank you, Kdvditters.