For ALU the speakers in the 1.1 are 3" square, and the mounting plate is not plastic, which may impact your thoughts on drilling larger holes.
You can use this as direct replacement - https://www.amazon.com/Visaton-FRS8-8-3-3-Full-Range-Speaker/dp/B0056BQA4S/ref=sr_1_2?crid=240QVVEPZVC3Z&dchild=1&keywords=visaton+frs8-8+3.3%22+full-range+speaker+8+ohm&qid=1622080725&sprefix=Visaton+FRS8-8+3.3%22+Full-Range+Speaker+8+Ohm%2Caps%2C211&sr=8-2 They do sound better, but imho not that much better to make it worth doing, this size speaker just isn't going to have much bass.
If you want to upgrade the sound you can do it one of two ways. First just replace the stock speakers with something the same size but higher quality. That might do the trick by itself. There is a whole discussion about 8ohm vs 4ohm, 4ohm will be louder, but some people say it may damage the system if it wasn't made to take 4 ohm. For example, the ALU 1.0 system used 4 ohm, 1.1 appear to use 8 ohm speakers, I do not know what is in the ALP... I would just use the same specs as what you take out.
Second way is get a speaker level converter and take the speaker wires and connect them to something like this -https://www.amazon.com/Rockford-RFHLC-Speaker-Signal-Adapter/dp/B009VTDVMU/ref=sr_1_5?ie=UTF8&qid=1540925155&sr=8-5&keywords=speaker+to+line+level+converter&_ga=2.56944810.1882133783.1621392273-325564800.1621392273
Then from the RCA jacks you now have add one of these mini amps, some have a subwoofer out on them.
Then just add speakers! The amp will power left, right and a sub! Again I would use same size if possible to keep from having to make larger cut-outs or whatever, and locate the subwoofer in the bottom part of the cab. You could also put an Alexa controller power strip in the the cab and plug everything to it (looping the cabinet AC back into the bottom as well if needed). Then drill a hole to route the power strips cable out to the wall socket. That should look pretty clean.
I guess with the RCA you could get a PC speaker system too, like Logitech Z313 or something, though not sure how I would attach the speakers and what not.