Tube amps and low impedances

Totally opposite:

Tube amps drop their output power as the impedance goes down and capable only to drive a high impedance loads opposed to the SS amps that have a large current delivery capabilities certainly depending on output stage configuration and power supply.

An output transformer for the tube amps is an interface to match impedances of speaker with output stage that in real case requires the impedance to be much higher than even 16 Ohms.
Tube output stages have no current delivery possibilities and mainly amplify the voltage. Thus with transformer output stages tube amps deliver same power to the different load values depending on output transformer capabilities to handle the low impedance loads for certain time.

For what ever it's worth, as I have absolutley no experiences with them, the tubed Walcotts are supposed to be able to handle low impedances. Some respected Audiogoners have praised them.

Another line of stable to low impedance amps is VTL and Manley (PP amps only)

Walcott amps are good for these kinds of loads they work well with electrostatic speakers also

Take a look into the Music Reference RM-200