One approach would be to keep your Luxman as the power amp and add a tube pre-amp, like the PrimaLuna EVO 400.
This way you don’t have to worry about driving your speakers yet you have the “tube sound,” which can vary widely but you can have a lot of fun with tube rolling to get the sound you like.
You also don’t have to worry about replacing power tubes nor doing periodic biasing of those tubes.
Finally, if it turns out the tube sound is not what you hope it would be, you can easily revert back to using your Luxman as an integrated amp again.