I don't have BT Infinity just normal broadband so I don't have that extra white Infinity box you have, but I do have the same BT Home Hub router.
My config is this:
BT Home Hub connects to internet and provides DHCP to my home network BUT the wireless is turned off.
TimeCapsule is wired to the Home Hub and only the TC is providing a wirelss signal for my MacBook, iPad, iPhone, Imac, printer etc.
This has the additional advantage that my BT Home Hub does not particiate in the BT FON network which allows passers by to use your BT Home Hub as a wireless access point. FON does not expose your home network but it does allow others to use your broadband bandwidth and I'm not paying for that BT thanks very much.
To do this you can connect to your Home hub at http://bthomehub.home or possibly at ip http://192.168.1.254 . From the admin screen Home Hub presents, choose "Advanced Settings", provide your login credentials. Then choose Wireless and there you can disable wireless on the Home Hub.
Then on on you Mac run Airport Utility to connect to your Time Capsule. Choose "Network" and set "Router Mode" to "Off (Bridge Mode)".
I'd like my TC to provide DHCP but I can't find a way to make the Home Hub "dumb" just yet.