I have the opportunity to pick up a second hand pair of the 328s at a pretty good price, and am currently running the 228s paired with a big rel.
What is a “pretty good price?” Personally, based on the performance I would not be tempted by 328s unless I could snag them for under $5K/pair.
I say that because Børresen X3s can be had for <$10K pair with a typical dealer discount. They have far less audible cabinets and higher SPL capability despite the “4.5 inch” woofers (which are really 6” woofers by any other’s standard.” They X3s would be a clear and worthy upgrade over your 228s, while the 328s will only surpass your current speakers in a couple areas.
I’d also consider a pair of pre-owned YG towers, especially since you already have bass reinforcement with the subs.