Speakers to pair with the Ars Sonum Filarmonia tube amp?

ProAc should work well. You may want to demo a pair.

Keep in mind that the Ars Sonus Filarmonia has an 8 Ohm x-former tap only.

There is a fantastic deal on a pair of the newest Reference 3A Episodes on Audiogon right now, with FREE shipping. They would be a great match for that amp. An easy 8 ohm load and 92db/watt/meter efficiency. I already have a pair that I have been enjoying for 5 years now, and I'm still tempted to grab them at his asking price!

Devore might be another good choice, although I agree Reference 3A is one of the first I thought of. Totem is another. Cheers,
Spencer

Here's another couple to look at.
http://www.fritzspeakers.com/sound.asp
http://tyleracoustics.com/pro_dynamics.html (Model PD10 or PD15)

Need to look at impedance curves to insure no dips in impedance below what the manual states / warns (4.3 Ohms ?)