I have the 550AX II and would say that the phono stage is excellent. Given my listening tastes and background as a musician, I do not find the amp to be "warm-sounding," especially when compared to the various tube components I’ve owned over the years. Speakers are Sonus Faber GH and while the Lux does a good job driving them, I still prefer tubes.
As many others have observed, Luxman build quality and reliability is superb. I suspect you will like the 550AX II. It runs warm, but much cooler than tubes of course. :)
A suggestion for an integrated which you might like a lot is the Wells Audio Majestic. I enjoyed mine a great deal but gifted it to a close family member. IMO, it's warmer-sounding than the Lux.
One last thing: I’m quite intrigued by the Ruby you mentioned and hope to audition one some day.