The problem is you need efficiency to really hear what the amp can do.
With any SET, your normal high volume listening level should not exceed about 20-25% of full power that the amp makes, due to the excess distortion that will occur. The distortion manifests as 'dynamics' due to how the distortion components interact with the human ear.
This is one of the reasons people often think or say that 'its loud enough'; its not because it actually is- the 'loudness' they hear is being caused by distortion, not actual sound pressure.
The reason this is so is that the ear uses the higher ordered harmonics to sense sound pressure. When higher ordered harmonic distortion is present, the result is that it sounds louder when it really isn't.
To avoid this, a more efficient speaker is needed. If you want something smaller, about the only game in town is a higher efficiency full range driver, like a Lowther or PHY.
PHY has offered an open back cabinet for their 8" driver that is actually not very large and isn't expensive. Its good down to about 60 Hz or so and sounds pretty decent. Its efficiency is about 99db with the PHY driver. I'm not a fan of PHY, mostly because the product is not well supported after the fact (we had to recone one once and getting the parts was a nightmare- PHY was being pretty precious about them). But if you really want to hear what a lower power SET actually does, you need this sort of efficiency in most rooms.
In truth a horn system of 105db or more would be better, but that is hardly 'monitor' sized.
