If you have the drives already then it's a no brainer to use for both. Clive S did this for years and run a Mill and Lathe from same Control box using a change over switch. Obviously you can't run both together but how likely are you to ever do that.?

Like Depronman says for a basic setup the Linux CNC Config Wizzard is easy enough to use and it costs nothing to try. You already have a working machine and know all the I/O pins so just try a Config with the settings for your Router and plug into a parallel port. Lathe is pretty much the same just less axis.