Since you mention you need this for your actors to practice with, I will assume it's for a musical. Check with the publishing company of the musical. Many offer a split
track CD. This will put all instruments to the left and all vocals on the right. If you can get one you'll need to
plug your output from the CD player into two separate
mono channels on the board. The
fader and AUX pots for one
channel will control the instruments, the
fader and AUX pots for the other
channel will control the vocals. The reason I recommend two
mono channels rather than a stereo
channel is that on most mixers, the AUX sends you're probably using for
stage monitors are usually summed
mono prior to the balance control (even on the
post-fade AUX sends). This means that the vocals will be heard on the monitors (and any effects returns) even though the
channel is balanced hard left. Using two
mono channels will work around this issue by giving you full control of the
fader and AUX pots of each
track (left and right) separately. All this advice is of course only good if the publisher of the musical you're doing offers a split
track CD.
Jeff