In the dialog box "Time Signature" click the button "More Choices..." and check the option "Use a different Time Signature for Display". Set the Display Time Signature as you like, e. g. 3/4, and click the button "Composite...".
You arrive at the dialog box "Composite Time Signature". This dialog box is a very flexible tool, allowing you to enter the composite time signature in 2 different ways:1) The "Numerator" method:
To beam all 6 8ths together, enter 0.75 over 1.
2) The "Denominator" method:
To beam all 6 8ths together, enter 1 over 2+4.
If you check the option "Use EDUs for Beat Duration", you will use the fact that
2048 EDUs = a half
1536 EDUs = a dotted quarter
1024 EDUs = a quarter
512 EDUs = an 8th
a.s.o.
When "Use EDUs for Beat Duration" is checked, the methods go like this:
1) The "Numerator" method:
To beam all 6 8ths together, enter 0.75 over 4096.
2) The "Denominator" method:
To beam all 5 8ths together, enter 1 over 2048+1024.
Peter