Will ARC VT50 45wpc tube amp drive B&W Matrix 805?

It should sound great. However, it depends on how loud they want to go...
B&W's are relatively efficient but won't complain with more power.

Abrew19

Elevick raised two good points re: B&W 805 matrix based on my experience.

They are a nominal 8 ohms but they dip to 4 ohms. I got the best performance with them by using the 4 ohm tap on my Push Pull tube amps. If used without a sub the high pass B&W Bass Alignment filter allowed for 42 hz bass response; otherwise its 52hz.
They are (-6db points / 35 - 22khz frequency response)
If using a sub you could set the cutoff just above the 52hz since they do drop off quickly below 52hz without the BAF.

fwiw - they sounded just fine with the lower powered tube amp a little less than 45 wpc; but came alive and sounded phenomenal with the 100 wpc push pull and 200 wpc OTL amps.
Cheers