I take various JPI engine monitors in trade to help keep the costs of upgrading down. I use these for cores for new 830 displays from JPI, quick replacements for 'bad screens', and for upgrades or complete systems for other customers. I only sell units that I would install in my own plane, and make sure you have the right harnesses and probes for your particular project. And I have enough parts to provide full replacements if needed.
Here is a description of typical opportunities for improving your system:
EDM700 basic, add memory, add fuel flow, add USB cable for downloads, add transducers - carb temp, oil temp, OAT etc.
EDM800 - add MP and RPM, get % power. This is a nice upgrade, and gets you plug and pay ready for a full EDM830
EDM730/830 - the displays are the same and you can start with a 730 and add transducers until it is a full 830.
EDM900/930 - these are OEM replacements. There are some transducers that are compatible with the EDM700's (CHT,EGT,RPM, FF), but your installer needs to be on board with reusing the existing wiring and transducers. If you can reuse the EGT/CHT harness and probes, it saves a lot of installation time.
Used EDM900/930's do come up for sale, but it costs $500 to reprogram for your plane, and it costs a fortune to replace some of the transducers (oil pressure, fuel pressure, etc). So buyer beware.
Contact me for anything you might need, even if you want to change out an existing unit for an identical unit with a better display or cosmetics. The factory is running out of displays, I have units with new displays in stock for a quick change. I've seen some really hacked cases and faceplates.
Aerodon