You can have two Subs connected to your Arc’s room, but you can’t have two subs connected to your two Sonos Fives, if they’re set up as a different room, and not as surrounds. Unfortunately, your post only says what you have, and not how you have them set up. 

Ooohh, so i cant have 2 sonos subs connected to the sonos fives?

then i will return it

No, two subs in a single Sonos ‘room’ can only be used in a home theater context, in your case, connected to the Arc. Since I still don’t know how you’ve set up your Sonos ‘rooms’, it could be possible to have each Five set up as a different ‘room’, and use both Subs, one connected in each ‘room’, then you would just group the ‘rooms’, which would work fine, I’d think. 

I have the Arc for itself, and im using the two fives together with the sub in “another room”. But i was hoping to add a second sub to my steroe setup where i listen to music?

well, Sonos just lost 799 euro, ill return it if i cant pair it with two sonos five and a sub…

I just came off the phone with Sonos, and the answer from them is:

yes, two Sonos Sub Gen 4 together with two Sonos Five gen 4 will work together for music?? But everywhere else i read, i see different opinions?

Since you’ve ordered it, wait till it arrives and try adding it. Then you’ll know, and can post an update here.