Yes you can use 4 ohm speakers in the saddle bags and they will not damage anything. You will probably have to fade to the rear 1 or 2 notches to balance the volume. There is a lot of threads on this here about it if you can find them. Thinking myself of upgrading myself now too, after hearing my buddies new 21' Fossgate systems much better base output and after going through 2 sets of stock speakers. Note: a 2 ohm amp actually runs a little cooler pushing to a 4 ohm speaker but not necessarily the other way around. Ideally to achieve max / optimal output of any amp you want to match the internal (ohms) of the Amp to the internal (ohms) of the speakers used.
I appreciate the feedback. The particular speakers this member used even says in the description "Not compatible with Boom II systems":
https://rockfordfosgate.com/products/details/tms57/So with that, just wanted to dig further. In the end if its safe to run and they sound better, I'm all about it. I understand I would lose the tweeter in each saddlebag as the Rockfords are only two way, but I found that tweeter to be a little harsh anyways.
Just throwing it out there because I don't know the answer... Why couldn't you use the '21 Rockford speakers on a boom II system if they are also 2 Ohm? I assume they are 3 way speakers with a woofer, mid and tweet? Is it just a matter of Rewire? Is it that you would have to change the speaker grills? Everyone says you can't, just wondering why?
I put a lot of effort into understanding that myself. It has something to do with physical fitment based on the amp and wiring. Three different dealerships have told me it can’t be done when I was ready to spend the money. I’m sorry I can’t offer more details, It’s been a while since I’ve visited that option. I really don’t understand why two different 5x7’s wouldn’t be interchangeable, either.