Folks do all the time. It is usually buried in a machine specific thread.

Tony D did an awesome research and write up on it for Williams pins years ago. I keep the link bookmarked.

http://www.dziedzic.us/wpc_speaker_replacement.html

I did my DW using Tony'a guide including routing out the base cabinet for the larger sub. Easily 1/2 the price of a packaged kit and sounds just as good(if not better.)

Just add a Polk PSW10 subwoofer under the game, you will be blown away by the difference.DSC01933.JPG

I have one under every game in the roomDSC01934.JPG

I went with the Pyramid 4108GS and Pyle PLG64 in my old Sorcerer and Grand Lizard and was pretty happy with the upgrade.
If I remember correctly the Pyramid set was like, $20(?) and I believe the Pyle (for two) was just under $30.
So, $50 to improve the sound on two classic machines as well as the small bonus of reducing a bit of the typical Williams SS "hum", was a win-win for me.

Check my "custom" NP speaker standoff posts too... (Patent pending patent pending )
image.jpg

The external subs sound great and have come down a lot in price but, visually- I like a nice clean floor underneath the games so I tend to choose the stealth sound install/upgrade for my pins.

i just put a Boxter 10" woofer in my GnR, and let me tell you, i dont need a shacker

also installed new 4" speakers in the backbox and a Pinsound card,that PS card is just WOW!!!!

I'll just leave this here: https://pinside.com/pinball/forum/topic/addition-of-boss-amplifiers-to-stern-machines

That is the addition of speakers, 2 pre-amped equalizers, and a Polk external subwoofer. Pictures, full description wire by wire, and 3 videos.

Good time to keep a look out on powered subs what w/ Black Friday just around the corner