"not sure if Magix is supported by the old SPM"
It sure is! I run both DOS and Win SPM on the same laptop. DOS SPM is better at the initial programming, where the system reboots several times when defaulting, setting the mode, setting the operators, etc. It just reconnects faster than the Windows version. Also, you can connect locally in DOS and remotely in Windows at the same time; great for programming networked switches.
One other tool I use the DOS spm with, is a Hewlett-Packard 200LX Palmtop computer. This is a checkbook sized clamshell computer, which runs DOS, has a serial port, and runs DOS SPM like a champ! It's small, but great for using when you just need to make a couple of changes or find ports in maintainence, etc.