What may be the best way to convert my Denford compact router to mach 3?

[JAZZCNC]

The controller it's self is not difficult to setup at all even for a novice, thou it must be wired correctly otherwise it can be damaged just like any other device incorrectly wired.
As to connecting to your existing hardware then I don't know enough about your machine to comment. If just a case of Outputs to control things on/off and inputs to monitor things then I doubt you'll have a problem because the CSMIO uses 24V I/O's which are common on many bespoke control systems.
CSMIO range of controls are often used to retrofit large industrial machines, both lathe and milling/routers. The IP-M being the baby and only 4 axis with reduced features, with IP-S being the Daddy for Step/dir control and the IP-A being the Grandaddy for Older anologue machines so if you have any chance at all these will give you it I'm sure.

Regardes the new drives and connecting then that is simple. If your wanting to use the existing drives then you'd need to check out what they require. Thou I suspect you'll get much better performance and easier conversion if you upgrade the drives.