The 824 product is just that, 8 lines 24 phones. you can't connect the first 2 lines in series because they don't supervise (mark each other busy) between the cabinets. In a severely obscure way, you could make 2 lines of a second 824 be extensions off the first 824 and grow the extension size to 30 (as in 8x22 and 2x8) but don't do it. You'd have other problems, like disconnect supervision and different dialing plans. For what you pay for a pair of disconnect modules and the waste, you can just buy a TD-1232 on the secondary market with 2 8-EXT modules for 8x32. YMMV.

As far as a TDE or NCP (the current Pana product) you'll find that you can probably buy the used TD-1232 box for less than the price of 2 new 16-port Single Line extension modules.

This is a Panasonic dealer question. We can tell you what to do, but not how. If you don't understand the concept, call your dealer.

Carl