@bzawa I don't think the 804 is a useful product. The 805 + two DB4S will give you more full mid-bass and lower extension for much less. You can use the app to pair them.
@speedysteve4 mid-bass output on the 702 can give my 802 a run for the money, better in some respect to tightness. The 804 is not on the same level. Below 40Hz, even the 802 could use help from subs.

