ARC DS220/450 Distortion Levels

There is very little in the way of bench testing of these "hybrid" Class D amps. I find the ARC pedigree always appealing. These things double down their output when presented with lower speaker impedances. But I seem to remember seeing one (and only one) bench test that implied that measured distortion once you get down around 2 ohms increases dramatically up to 3% or so which I would think would be umm, not so good a thing. I would be using the amp (probably the 450) to drive Thiel 2.4s which for a wide portion of their frequency output present a load of around 2ohms, sometimes dipping below that. Thoughts?
If it's in the bottom frequencies domain, it's nothing to worry, In the midrange it may be audible. Check your speaker frequency/impedance map.
By bench test do you mean a test performed by a magazine? Audio Research has a much better facility than any magazine could ever dream of having and more intelligent people performing the tests. Why not contact Audio Research?
Also, your Thiel 2.4s have a minimum impedance of 3ohms not 2ohms and below.
Not an issue with the DS450. I use one to drive my Revel Salon 2s, which are fairly inefficient and power hungry, without a hitch.