You could be reading too much into the sensitivity rating of the speakers when you should be more concerned with how much of a load the speaker presents to the amp. Generally speaking a 4 ohm load draws twice the current of a 8 ohm load. With any amp the maximum power it can deliver depends on the current and voltage. Some of you may have seen this expressed at P= I*E or power = current times voltage. A low impedance load will mean more current flows and based on the voltage that means more power demands.
Also keep in mind that the quoted impedance of the speaker is not constant across the frequency range. Swings up or down a few ohms are normal depending on frequency. So at 2 ohm swings for example you would be drawing even more current into the speaker. While the Axioms can certainly handle the current, the question is will your amp be able to supply the increased power demanded by the speaker. While much depends on how loud you want to play the speakers, you will find the limits of your amp before those of the speakers.
At very low volumes you may not have a problem but I suspect at reasonable listening levels or during sharp transients you would clip the amp or at least have distorted sound with the 80s. Contrary to what many people think underpowered amps driven to clipping are more likely to damage speakers than having beefy powerful amps. The 8 ohm 60s would be a better choice and make less demands on your amp at moderate levels. Besides, I think it has the best tonality of all the speakers in the lineup and would likely produce an lovely airy midrange with that tube amp.
