You are correct with your first question. The "interface box" is the DAC, but it will not work with all software. I don't use iShow so I can't tell you all of the software it works with, but it will work with Spaghetti. Check out their web site. Here is the link, its what I use.
http://hingednewt.com/Spaghetti.aspx
Yes your DAC does use the ILDA standard connection. That is a good thing. That means that it will work with any laser and/or scanners you like. Also here is the DAC I use. It is compatable with lots of software out there. Its great for beginners, the right price too. Another Dr.Lava product. Here is the link.
http://www.photonlexicon.com/forums/...te-Controllers

Your second question: Yes you will need to replace the drivers for the stepper motors. When you buy scanners they come with drivers/amps tuned at the factory for that specific scanner. Even swapping a scanner from the same company made at the same time can cause problems. Tuning a scanner amp is more like an art than a science. It takes practice and patience to learn. That is why scanner amps are factory tuned and kept with the scanner as a set. Several of us know how to tune amps if you ever need it done.

Lazerjock