If you are used to class A, it is hard to be happy with anything else. teh marketing literature will always say that it is as good but my experience says otherwise. Most class A/B generate very little heat, yet they claim they operate in class A up to several watts. Draw your own conclusions. I've drawn mine. they they aren't positive.
your 99dB speakers could operate with a very low wattage amp. I have driven my 98dB speakers with a 2.3 watt decware amp with no problems. I find that an SET tube amp generally puts very little heat into the room. I don't even have air conditioning. The exception is the 6C33C tube that runs hot. radiated heat goes at Texp4. The 6C33C runs about twice the temperature of a normal tube so that is 16 times the radiated heat.
If you don't want to go tube, then there is the first watt which sould work fine.
There are a lot of people that will tell you you need more power they fall into 2 categories.
1. Dealers who want to sell you a more powerful amp. they want to disqualify most all SET tube amps so they say "you need at least 20 watts" or something similar.
2. People who repeat what the dealer told them.
Jerry