I’d humbly propose widening the lens. Assuming legit manufacturers, etc, a $150,000 preamp+amp(s) combo will always sound better than a $5000 integrated. It just will, even to the most jaded among us. Sure sure, you could have your quips, but it won’t be a serious comparison. So, in a sense, “a lot more expensive” usually does sound better. Turning to the OP’s specifics, comparing an $8000 amp to a $5000 amp could be pretty much like comparing a Coke to a Pepsi. (Except without the decades of history proving that Coke is better.)
I think about it in categories, just as a rough guide. 5-10k amplifiers, for example, are all on the same footing. Use your ears. 5 v 20? Decent chance 20 wins. 5 v 50? I’d bet a chunk of cash that 50 wins.