Sometimes this can be a tough concept to understand- How about if we approach it from a different angle?
You put your JBLs up on eBay.
The winning bidder declines the package.
You are out the bid, you are out shipping and packing expenses, and you are out a fee for return shipping.
For an individual, that can get pricey. You may be out the $20 shipped, $20 return shipped, and any expenses for packing.
You are also out your time. And effort.
This applies to the seller you bought the other JBLs off of, as well.
Big stores sell in giant volume- this cost is pennies to them because they sell thousands of items (most accepted), compared to a lone individual like yourself selling an item here or there.
Amazon sells thousands of packages. You, and other eBayers, sell only a few. A return or two on thousands is less traumatic than a return or two on say a dozen items.
I hope that helps.
Oh- and even if you do it at Amazon or a big store, it does raise prices for everybody- though that can be a mere fraction of a cent to a few cents. But yes, it does effect overall cost.
Now, back to your original theory-
Yes, 8-ohm speakers will be easier on your gear in general. Overall sound may, or may not suffer slightly, but the load on your gear will be an easier one.
Now, I do not know if you understand "clipping" but look that up in regards to amps and speakers. This will also help you in preserving your gear and help you provide your gear a longer life.