You need to divorce you wife or
your SET.
That unit although rated at 8 watts, has really unacceptable distortion over 1 watt. In addition a speaker must not go lower at any point than the rated output transformer tap, and should be twice the impedance over most of the range.
That really rules out any speaker with a crossover network. You really are pretty much limited to a Lowther driver. The
PM2A is the most favored for that amp. It has an enormous 2 Tesla Magnet and a sensitivity of 95.5 db 1 watt 1 meter. In a good horn like the Medallion 2 which was designed for that driver it has a decent bass response to 40 Hz.
As long as you hang on to that amp your wife will not like your choice of speakers. May be you should move your rig to another room, or may be your wife.
For any decent results from that amp, Lowther is really you only option.
Lowther Medallion Horn
If you have gone down the rabbit hole you have chosen, then you can't go down a mole hole.