My experience with Luxman was the same. That was in the late 80’s. I hated every minute with the Lux. It had no bass line , just a constant thump from the bass drum.
I can’t comment on something 40 years ago, but in my recent memory, of the past 3 years or so I’ve never ever heard the Luxman’s be bass shy. The Luxmans I know of have extension in spaces both in the treble range as well as in the bass. I am more likely to believe the BHK lacked treble, and that Luxman is more well balanced. 😁
But seriously, if the effect the OP describes is so severe it makes him want to suddenly add a sub I’m going to question whether this is really due to an amp swap. Room acoustic issues like adding more reflective elements in the room, or taking away bass traps are the sorts of things I’d suggest first. Next, if this really really is happening, swap your cables for some Mogami 3106s. On my Luxman I had to turn the bass DOWN after I put this cable into my system.