I would recommend you go to an audio store, even if travel is required and listen to an Audio Research I/50 or LS28/VSi 70. The contrast with your Luxman will be profound. It will also tell you something about what you should do. If you love the sound… then trade your integrated. If you want to move 10 - 20% towards the ACR sound add a warm tubed preamp, if you want to move another 10% add a tubed DAC. If a movement towards that sound of 35% or s isn’t enough, then swap integrateds.
I recently compared three integrated amps, Luxman, Pass, and Audio Research. The contrast was striking… and pretty stark. The Luxman was detailed and crisp but without musicality and warmth, the Pass was detailed with a much more natural presentation and palpable rhythm and pace (think foot tapping musicality), and the Audio Research was warm and so emotionally engaging it took my breath away. Be aware… I really love ARC for their sound quality… so it is not surprising my reaction. Some might like the greater slam of the Pass (INT-60). The Luxman looked cool.
I was helping a friend choose… a newbie. While he liked the ARC, I recommended the Pass as it was his first high end purchase… I thought he needed to go through the great slam stage that he could impress his friends with. But he actually thought about it for a couple weeks and bought the LS28 preamp and VSi70. I was shocked and know he will have these for a couple of decades.
Anyway, I think if you listen to what I would consider the possible end point… you could judge how big a move you want to make.