For this I use a button - actually two buttons. If you use these buttons you will need to revise the location of foobar2000
This one adds all marked files to current playlist:
-----
TOTALCMD#BAR#DATA
c:\TotalCmd\apps\foobar2000\foobar2000.exe
%P%S
c:\TotalCmd\apps\foobar2000\foobar2000.exe
Foobar|Play marked
c:\TotalCmd\apps\foobar2000\
0
-1
-----
Just copy lines between the ----- and paste to the button bar.
I use this one to add to the current playlist:
-----
TOTALCMD#BAR#DATA
c:\TotalCmd\apps\foobar2000\foobar2000.exe /add
%P%S
%!Cmc:\TotalCmd\apps\foobar2000\foobar2000.exe
Foobar|Add to current playlist
c:\TotalCmd\apps\foobar2000\
0
-1
-----
Just copy lines between the ----- and paste to the button bar.
2 rus73
If it doesn't work for you, you're doing something wrong.
Note: here is a solution for foobar2000.
It works for other programs only if it support many files in single instance and many file names in command line.