MusixTeX does not work with LaTeX, and works on plainTeX.
If you would like to use MusixTeX with double columns,
I think the best method is to use the macro "eplain.tex",
though many macros exist in the Web.
By "\doublecolmns", TeX starts with a page of double columns.
By "\singlecolumn", it goes back to single column mode.
You can use "\triplecolumns" "\quadcolumns" also.
When you want to control the lineskip length under "\doublecolumns",
you should insert "\baselineskip=20pt", for example,
each beginning of paragraphes and displayed formulae,
and each end (= beginning of its following sentence or equation) of displayed formulae.