Hi, I have not found a way to apply a common theme on both store fronts, may be because I only subscribe to the basic eBay store.
But probably because eBay and Auctiiva are seperate companies and Auctiva is probably seen as undermining eBay with their many free options that eBay charge for.
So it is probably confusing to buyers seeing two totally different store styles but there does not seem to be anyway to reconcile the two.
Perhaps a direct support request should be filed to ask about it if you are in a hurry otherwise I am sure others will reply soon.
Regarding your two store fronts I have the same problem. One good the other ho-hum.