I think I've almost got this.

I've tried (no work)
1) connecting line 4 - DSL Line - directly into my 616
2) connect my DSL modem to an output port or port and ATA

What you are suggesting is:
1) Connect line 4 to a splitter, the modem does not have a "phone" jack
2) one to the modem, one to the 616

Correct?

I sort of tried this by connecting the line 4 to the 616 after the modem connection in my main panel and it did not work - sounds the same, but much more straight forward. Can't wait to try it.