Jaspette, you asked what you would need to do.
Assuming that your downloaded files are not cdg files in the sense of the correct files used by Microstudio.
Anything that can be played on the computer can be recorded as, or converted to a wave file. The computer can "record" any sound played on the computer and save it as a wave file. Most sound files can be directly converted to wave file. Once you have a wave file you can use KHPRO to add lyrics and create cdg files, which will certainly work with Microstudio.
I don't know how desperate you are in Phoenix but maybe you can use this info.
I heartily recommend the MTU Karaoke products including Microstudio, KHPRO, Vogone, and Keyrite. I don't know about Hoster but it seems to also work wonderfully.
Good Luck