High end digital Vs lower end acoustic?

I've been playing for around 2.5 years, with a Roland FP-30X. Also have two kids learning, between us we learn/pay a mixture of grade (ABRSM) 1-5 material. I'm starting to appreciate some small limitations of the FP-30X, the action is quite noisy - especially noticeable when someone plays with headphones. The onboard speakers aren't brilliant - not super loud and headphones sound a lot better.

I'm starting to think about getting a new piano, but struggling to decide between a high end digital, most likely the Roland LX-6 (~£2500) or an acoustic in the £3-5k price range. What am I looking at for a used acoustic in that price range? Yamaha U1 or U3? Pros cons? We'd keep the FP-30X for headphone practice.

I guess what I'm really asking is how an LX-6 compares to a <£5k used acoustic?