Is 45W enough power to drive B&W N805?

I ran a pair for a while with a Cambridge Audio A3i 50 watt integrated amp. Worked fine at mid or lower volume levels. I think the "official" power range of these speakers is 50 to 200 watts per channel at 8 ohms.

if u r running clean not over rated 45 watts per/ch,,, u should not have any problem...go listen to VT60

Haven't heard them with many tube amps, but I can tell you to be careful. I did hear them with C-J CAV-50, and it didn't have enough to drive them(by any stretch of the imagination). The current demands were too great for this intergrated amp(just like the MV-55 power amp) to handle. I think that maybe an amp based on 4 EL-34's might not have the guts. You might try one using 6550/KT88/KT90. Amps based on these other amps tend to be more expensive, and not as magical. Maybe look at the bigger used C-J, Quicksilver, SF, AR, etc.