Good Tube amp to drive B&W Matrix 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.

I used Jadis JA30's on them and they were fantastic! I had no problem playing them at loud levels and they controlled the bass well. Everyone who heard this combination couldn't believe it. The quality of the amp is very important. I don't think most 30 watters would do the job.I use a MAC MC2000 on my Nautilus 801's and it is a very good combination.