Good Tube amp to drive B&W Matrix 801's

Rocky, I owned this speaker years ago and the Matrix are very current hungry and in my opinion are better served by a high quality solid state amp that can control the 12 inch woofer. Tube watts are more powerful than the stated power rating, but tubes don't seem to have the control of solid state. If you don't mind a looser, more full bodied bass sound then it might work. I would suggest a demonstration. I have heard the Audio Research 600's and the big VTL tube amps on Wilson MAXX and they did a pretty good job, but not a good as the Krell did on my B&W 801's.

Vtl 300's big time power and control on the lows

As above, you'll need extremely high energy amps to do the job well -- tube or ss. As noted above, you'll be easier off with a transistor than a tube -- if only considering the cost of tube watts.

Is there a conversion factor for tube watts vs sold state watts

The conversion rate is, well, 1:1, i.e. when your tube amp manufacturer quotes 50W, he/she means 50W.
Don't confuse the sonic qualities with the energy ratings -- nor the spkr ->amp interface characteristics with the electrical properties:)
There are reasons why we perceive some tube amps as being "louder" than some equivalent output SS amps -- but the "conversion" rate isn't one of them! Cheers

nothing less than a mac mc275 mklV.