The things you'll gain from π Speaker designs are dynamic range and in most cases, deeper and truer bass. The one π is about the same on the bottom end, but all the larger speakers go deeper than single drivers can. The other thing is that you really can't push a 20 watt part very loud, so dynamic range is limited. Twenty watts is about 13dB over one watt, so whatever the W/M sensitivity of the single driver is, add 10dB and you have maximum output. π Speakers will startle you with their authority when you compare them. But that also assumes that you drive them with some power.

Considering that you'll use a low power tube amp, that takes the dynamic range issue away. You're not going to hit the speaker with 100 watts, so that's a non-issue. That leaves you with bass response. In this regard, you'll find that something like the relatively simple and inexpensive two π or two π tower gives you deeper, smoother bass. The new eight π uses the same tube-friendly midwoofer, and it's horn-loaded through most of the audio range, so that's an attractive option too.

The Theater Series four π is the most popular large π speaker. It is very tube friendly, and struts its stuff when belted with a couple hundred watts. So it does well at both low power and high power levels, is very versatile and sounds great too. The Thermionics are also very popular, but they are large. The Thermionic three π is similar to the Theater four π speaker, but it doesn't handle quite as much power.

I really like the Stage Series, but I don't recommend them for use with tube amps. It is great when you have a powerful system, and it sounds nice at medium and high power levels. But it isn't particularly "tube friendly." I will say that Stage Series speakers sound excellent on Bottlehead Paramour amplifiers, but that is an unusual situation. Most amps will not like the load, and will have reduced and/or peaky bass when used with Stage Series speakers.