Hi, TotallyT4KTout
If your on a slim budget and the Boss 5 machine will Re-set & lockup the stepper motor's, As MachineMaster stated, You can inter-face Mach3 with no great Issues, Both the Series 1 and 2's machine's, They will still function manually, E-Stop, Spindle On Off, etc... with the old computer board's removed.
It's a really nice machine to convert, Any way you approach it. Quick change tool holders, Ball Screw's, Coolant Table and Limit SW's, Already Installed.
The method I used is basically the same, In fact you can remove just "One", 8 pin plug-in Connector 6 Wire's and Run Mach3 in what I call role-over mode, It's (Max NC-10 Wave Drive Mode) and has preassigned pin out's in Mach3.
I've used it also for 10+ year's with several Boss Mill's with software that works the same as Mach3 in "Max NC-10 Wave Drive Mode", Just been to Lazy/Crazy or Sidetracked to install a Faster Computer to Run Mach3 in Window's Environment.
Edit: In fairness, I Should Say, In Testing I've Done, Mach3 Appears to function the same way as last Paragraph Above, Never like being out on a limb or working on a high wire, The Fall can be Bad Ether Way.

Just some Thought's, Chip