Who here has gone from d200 to 400?

[Zappydev]

Also, I knew if I go this route, I’d have to pick up a digital coax cable, but I see mention of a 3.5 mm link cable “for commands” also in some threads and on the “what’s in the box” devialet website.

What does this 3.5 mm link cable do exactly?

Hi - it allows you to make use of the inputs on the Companion in addition to those on the Master. If you don't need the extra inputs, you can do without the cable.

btw - many years ago, I went from D200 to D400, and for me it was worth every penny. Then again, after buying my Od'A ( 8 years ago now - time flies ) I was more than satisfied with the subsequent CI upgrade that came along a little later (although that one was a freebie).

If you like what you already have, then either or both upgrades will bring you even more pleasure.