Speaker wants 100 watt RMS. Is 40 watt tube OK?

90 dB sensitivity, 8 ohms, you should have no problem as long as you don't have a huge room.

onhwy61  said: "If the loudspeakers are 87db sensitive -  Monitor Audio loudspeaker is a 4 ohm load." 

That is not correct the speakers are 90db and a 8 ohm load, 40 tube watts per channel should be plenty if not in a large room or at head banger volume.

Sounds like a nice setup, enjoy ...