Maurik
Quoted from ccbiggsoo7:wondering if maybe I ought to just go to best buy or ebay and try some of their speaker options. Notice a big mark up on stuff if its pinball related for some reason!
Keep in mind that the resistance (Ohms) might the different. Somebody over at the Metallica thread fitted Clarion car speakers inside Met. Not sure if he needed any additional hardware.
https://pinside.com/pinball/forum/topic/metallica-owners-thread
I have a Met Pro with FF with 10” and it sounds great. I don’t have any experience with external subs on pinball machines but do have with home theater setups. Cheap subs like the ones mentioned all over Pinside generally don’t sound very good. Obviously they increase the overal quality with stock speakers but in my opinion they add too much bass if you aren’t careful enough with the volume.
Backbox speakers sounds SOO much better from FF but the sub really improves it. Unfortunately on Met the SAM system is only mono and uses only lower quality audio files. 
Like said before buy the volume control as well. Leave the extension cord and coin door mount. You’ll set it up just once and it’s fine.
The 10” is delivered with anti-rattle tape but I didn’t need it. No rattle at all.
