A V6 converts into a 360-master and retains its hard-drive storage.
A 360-mini doesn't have a hard drive of its own, and slaves from the master box. So you're effectively asking to swap a master for a mini.
It may well be that the second box is included in your package, but your bills & contract should help with that. What do they say? Feel free to post up a redacted (personal details blanked out) copy if you want someone else to check it.
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