Replacing speakers in Lat-1's

Can I put better speakers in cabinet to get better sound?
There sounding better. OOOps there brand new. Need to be broken in along with the new tweeters.
the answer is- Yes you can improove.and a lot. but-
1)I would strongly recomend not to change xover unless you want to fine tune speakers a litle. you can change tweeter to 70000 series ring radiator you will get better dynamic ,more imediacy insound(just measure/calculate krell xover voltage divider or serial resistor to ensure the same eficienty with THE SAME voltage divider values)

bass drivers also can be changed to better ones (22W) bass will be fuller and more punchy not hard sounding .

what you can not change its midrange.yoiu can but its likely 99% that it will sound worse. even the same drivers with 1mm shorter coil will have diferent response and will kill krells enginiers sound conseption.

as for my self I am using aluminium enclosures also and they deserves very best drivers, better thant theese in krell Lat1 IMHO
Have a pair of Krell LAT 1 speakers and have looked everywhere for replacement 8” woofers  Scan Speak Type 21W/16555-2 16 ohm speakers Called Krell and scan speak none available. I’ve looked everywhere and can’t find any.  Any suggestions on something that would work without having to modify the speakers. Thanks, Russell 
I realize your post is old but I have 4 new old stock 21w 16555 speakers available for sale.    I purchased for a project that I never completed.