Well a budget and other goals or limitations would be helpful.
Rear channel speakers aren't as demanding as front or center. So you probably don't need anything terribly expensive.
Subwoofers are basically a question of cost and size. Horn subs of one sort or another can be extremely powerful and efficient, but tend to be large. You can go much smaller, but require more power and more expensive drivers.
I think that for just music a pair of speakers is enough,
Only if you have SACDs or ( are Blue Ray multichannel ? )
And I think that for a pair of speakers, more than a source ( speaker)
per frequency band is enough.
The Statements scare me, as also horn ( subwoofer ).
Next time chose a better speaker ...and go bi-channel .
for me it's difficult to think of more than two ( coherent or not) sources of sound playing together; I mean, it's a huge job to make 2 channels working and produce excellent results. And i don't know how others apply their excellence mark criteria.
If it's for budget...well the Statements use woofers with foam surround, right ? Usually it has to be changed every 10 years ( or maybe not ).
As for the multiple woofers...I'll have one, thx
Multiple woofers are allowed only for sub-bass duty, as the source doesn't need ( and can't ) be recognized and located . For an instrument, I don't like to have it spread all over, it's a matter of attribution and knowing the location of the sound, where it's coming from . And who produces it .
Other than that, I don't have any clue of where to start from
A classical 3 way with woofer-midrange-tw might be more appealing.
Or two way ...with a waveguide around the tweeter.