I am in the UK and managed to pick these up used for around £2000 GBP around 3 years ago. The Sigma are the passive bass unit version of the IRS Epsilon - that model featured a complex servo control system for the bass, whereas the Sigma operates conventionally. They operate in a partial and controlled dipole configuration, with a second EMIT and dispersion from the EMIM facilitated from the rear of the speakers as well as the front.

To provide context I do have a real liking for large panel and ribbon type speakers. I've had Magneplanars and Apogees and currently also have a pair of Kappa 9 speakers that I also really love.

To put it simply, these speakers are as good as the quality of high power signal you can provide them with. They are superbly integrated with fabulous air, transparency and great soundstaging and imaging. There is no discontinuity between drive units and the speakers deliver a wonderfully smooth and even, but also very extended response free of any noticable colourations and resonances. The EMIT and EMIM units are well known and rightly much lauded - they provide brilliant speed and resolution through the high and mid-range without any brittleness or harshness (unless that is on the recording of course), and this is coupled to a very natural and rich sounding lower midrange and excellent quality bass that extends down to around 30hz. Should avoid ussing with too laid back and warm sounding equipment, as the speakers could sound a bit heavy and laid back in tone in those circumstances.

The speakers are big, very heavy, need space and do need, as is customary with the Infinity IRS range, lots of good quality power and current to sound their best. I have been running them with either a pair of massive Conrad-Johnson EV 2000 stereo amps, bi-amping, or more latterly with a pair of Sumo TEN/M monoblock amps. With this kind of amplification the speakers can really sing, but be warned they are ruthless in terms of revealing the quality of the source material and of the partnering equipment,

All in all, beautifully built, true reference standard speakers that combine panel like transparency and staging with real punch and dynamics - meaning they really can deal with any type of music effectively - just sit back and enjoy.