Just found this thread, and I have experience with both Ohm and ERR from Decware. Apologies in advance for lengthy post.
I own refurbed Ohms - 2000 driver in 100 cabinets. I have attended Decfest the last two years, and at the recent 'fest I had a nice, long visit with ERRs. (Also Decware's HR-1 - more on that later.)
My ohms are far from optimally set up (front and one side wall are basically missing, meaning speaks don't have proper support balance), and I have some modes in my listening room, greatly lessened by two homemade bass traps. Decware's room basically doesn't hold in bass, so they don't have any modal issues there. I have a high-current, but far from audiophile, Integra SS amp and a lousy Blue Ray player connected by HDMI. At Decfest, ERRs were fed by superb tube amplification through nice ICs, and sound was sourced by a modded (tubed) high quality CD player. It's obviously an uphill climb for the Ohms.
Decware is a three hour plus drive from home, so comparisons were off of memory, so that tells you my impressions are not to be taken too seriously.
My Ohms have cavernous, awesome bass power, clean and very deep (I'd say into the 20s, though maybe not lower 20s). Sounds like a high quality subwoofer is in the system, with almost no boominess (and bass traps help). They have detailed highs that are slightly rolled off, making them very pleasant to listen to. Extremely smooth.
I listed to the ERRs nearfield (they were better that way), whereas the Ohms are a good 9 feet from my listening spot.
Essentially, the character of the sound between the two sets I found to be very similar. The ohms go a little deeper (only a little), and sound like bigger speakers. They have a more powerful sonic signature. The ERRs are a little (only a little) more detailed, with a slightly higher quality tweeter. They might be a little more nimble, though at the cost of some awesome power in their sound. All of this assuming the associated differences aren't the real reason for a variance. But, essentially, I found them to be extremely similar. Both sets are a joy to listen to.
Taking a step up, Decware has HR-1s, which are essentially the ERRs with an added midrange driver on the front. These are the best sounding speakers I've ever heard. They have all the smooth velvet and envolopment of the omnis, but they add a more direct, involving punch from the direct midrange driver. Best of both worlds, and worth it to drive out to East Peoria to hear them if you ever get the chance.
I will post again later with more detail on the build of the ERRs. They have just been taken down off the site because they are re-doing them due to changes in parts availability. I've spoken at length with Bob Z (builder of the speakers, and a true gentleman) about them, so I have some notes that may be of interest.
Cheers!