Dan, I went with Alpine Marine in mine. I have two pairs of Their 7" marine speakers, and two of their 10" subs. Smalls speakers running off a old school Aura Sound amp, subs off a big old school Fosgate. Budget system and it cranks.

I run 4 x 6.5 Rockford Fosgate speakers along the back seat and run them off a 500w Rockford Fosgate amp, then I have 2 x 12" subwoofers up in the cuddy that run off a 1200W Rockford Fosgate amp, It sounds great in my 270 Convincor till I throttle up, Then you really cant hear it. I also have a switch for my amps at the helm so I can turn the amps on and off when I want to and run the stock speakers off the head unit....When putting the system in I bought all of my wire and distribution blocks off of Amazon, I would research a stereo supply company and then cross refrence that number with Amazon and saved a TON of money on wire and stuff, I mounted my amps up in the cuddy so you need 4Ga to go all the way up and back to the batteries, Check with Amazon, you will save a few $$$$$ JMO. Good Luck!!

If you have 6x9 holes, stay with 6x9. They will deliver much better mid's than a 6" round. Car guys like the 6" because they are compact. Inches rule in a boat whether its engines or speakers!
Properly amplify them.

Subs are going to take a knowledgable hand for proper box work which makes all the difference.
Try to go 12" if they will fit under the seat.

Babb speakers are now DC Gold...great sound and can handle alot of abuse :whistle: not that I abuse mine

Great advice given here. If you can enclose your speakers it will make a world of difference. Much warmer tone. Running a #4 wires to the front is a good idea too. Don't scrimp on the speaker wires #12 copper at the least.
Just upgraded mine to jl's 6.5 in the back and kept the Poly 8's in the cockpit. Had Alpine in the back before. Love the bass and mids that come from jl's little 6.5's. Used a jl 400/4 to power the 2 sets and a Sony marine head unit with remote. Waiting to hear the new 8.8 that jl just came out with. They claim they have so much bass that you might not need a sub. Went to West Marine because of their no questions asked extended warranties. As long as you don't run over it with a car or bash it with a hammer they will just hand you a new one when the old one quits working. Cheap insurance... Very happy with my new system.
Good luck with your new install.

EBAY!!!!! or AMAZON!!!! Once you find something you like, I saved a ton of money that way when I did my boat last year.

Jl audio marine is the way to go I installed a couple of sets of the 7x7s and 8s plus the tweeters in my brother inlaws 27 tiara cruiser and it is all powered by Jl amps and sounds absolutely awesome just as if u were at a concert it's crisp clear and loud as hell placement is also key we used some factory holes plus made are own

I have JL 6.5's and 6x9's in the cockpit off a JL 500W amp and 2 12" subs in box's in the engine compartment off another JL 350 with 6.5's in the cabin of the Pioneer head. It is the best sounding mobile audio system I have ever heard. I am pretty fussy with my audio. It's the only system that can play the 33Hz section of Also Sprach Zarathustra the way it's meant to be and play the trumpet solo with amazing clarity. The first time I played it in my driveway, my neighbors the next street over thought it was an earthquake.