I have a DK40i with an expansion cabinet, it currently has these PCBs:

Base cabinet - TCOU1A
Exp S04 - PDKU2
Exp S05 - KCDU1
Exp S06 - PIOUS2
Exp S07 - empty

So, we currently have 24 ports, 12 from the base, 8 from the PDKU2, and 4 from the KCDU1

We don't need the extra CO lines from the KCDU and would prefer to get 4 more ports. From my reading it seems like I should be able to swap the KCDU for a second PDKU2.

I would like to just pull the KCDU and swap a second PDKU2 into S05, is this kosher?

That combo would work along with others. There can be a maximum of 28 stations (24 digital).

Oh man, I never realized that it was 24 digital stations. Looking in the General Description document for the 40i, it shows up to 28 DKT phones, which I thought required digital stations. Am I missing something?

Thanks for your time.

I just checked my documentation and you are correct - a maximum of 28 digital keysets.
Sorry for the misinformation.

Replacing the KCDU with a PDKU would work fine giving you a total of 28 station ports if you have a KSTU card installed in the base cabinet. Adding an additional KCDU would also work.

No problem. Thanks again! I'm going to have to check, but I'm fairly sure you're right about having a KSTU. The PCB markings in the base cabinet are a lot harder to find/see.

Yep, the KSTU's four analog lines are used for VM, which leads to my next question, but that's for another thread.