I own the Luxman 590AXII and it powers Harbeth 30.2’s which have an 87db Sensitivity (yours are 90 I see) with no problem. I can get well past 95db loudness when cranking it. There has been some discussion about the fact that although Luxman says it’s pure class A 30 watts into 8 ohms, 45 at 4 Ohms, third party measurements have also claimed it does switch into Class A/B above 30 and outputs 90 watts in A/B. Perhaps a dealer will let you try the 590 and switch it out to the 507 if you feel it’s necessary?
I don’t worry about it however, the 590 has a warm, but clean sound, it is clear without being sterile or bright. Great headphone and MM/MC preamp built in, I personally like the tone controls, and for me it drives my speaker fine.
I have never owned B&W speakers, so I can't tell you if it's a good match with them. I have heard PASS, Hegel and other integrated amps and they all sound great. Just a personal choice at that point. Hope this helps.