Unless they do something to "deepen the freq response & output" (aside from fixing the defect of which I know nothing about), I'd recomend you take the offered JBL.
This, if you are forced to take just one or the other. Of course just my opinion....
I highly doubt they would re-design the whole sub considering the cost that would be involved. The most easy/cheap fix for what ever the problem, is what will most likely been done.
Just a good guess....
If your getting the matched wood veneer of your other Wharfs with the sub and this is extremly important, then you will have to make the decision.
The Wharf sub your looking at drops like a rock around 30hz and the bass quality and output is nothing get excieted about. The Same Money would buy you "much better bass" in another sub product.
The power cube series is a week point in the speaker system if going all round Wharfs, then using a power cube to fill the bottom end...
You also know already what the JBL will do.
If you have not already, you may try to find all the user/mag reviews you can to read up on what others think of the P-cube your waiting on.
It may make your decision a little easier.....
Regards
Geoff