First Watt: current vs voltage

F1 and F2 are the two current source amps. I would recommend reading the 6moons reviews to get a good feel for each model. A First Watt dealer can also be of great help. Mark at Reno HiFi is a great guy and has an excellent return policy so you can see what works best in your system. He usually has most models in stock.

The First Watt amps are great. I have tried most of the F models, with the current source models (especially the F2J) and the F3 being my faves. But of course this is with my speakers and my listening preferences...

Roscoelli is right, 6 moons has extensive reviews on every First Watt model and compares/contrast each one.
The current issue has a complete review of the latest S1(SIT) First Watt amplifier.

The equation for Power is Voltage times Current. Audio amplifiers are power amplifiers. Speakers only care about the power delivered to their load. Amplifiers are rated in a maximum power delivered into a specific load. The amplifier only cares about the load that it needs to drive it's power into. The First Watt amps could care less what type of speaker they are connected to as long as the load is 4 or 8 ohms and that the load is fairly linear. Most of the First Watt amps are lower power between 5 and 25 watts. What you should be concearned with is speaker efficiency whether it is a single driver speaker or multiple driver speaker. The First Watt amps are the solid state equivalent of SET Tunes amps and indeed they have a similar sound. Single driver speakers happen for the most part to be very efficient. Nelson Pass happens to enjoy tinkering with single driver speakers in horn configurations but make no mistake they can drive any 8 or 4 ohm speaker with an efficiency greater than 92 dB at pretty good levels.