Hi, sorry for the late reply...I've been travelling.
The BEL amp I'm referring to is the Brown Electronic Labs 1001 Mk V. It's been in production since the 70's.
I've compared it to a lot of different amps over the years in various systems. It's simply the most natural sound I've heard yet. The sound is less dependant on the amp than on the pre-amp and source you put in front as it can resolve everything it sees. Also, you will want BEL cables as well so you can get the best out of the system it's used in. Try it...you'll "see".
I compared a MkIV to the Dreadnought I several years ago. There was no comparison. The BEL smoked it in every way. The new Mk V amps are an order of magnitude better than the older Mk IVs. So if this amp is in your price range ($3,895) it should satisfy your requirements without a problem. Just remember that the associated gear will make a big difference!
As for impedance, that is relevant with the Theta amps to some degree. You would have to try the BEL or another amp that doesn't have Zero Negative Feedback to see if it's a difference for you on your speakers.
IMHO, if you can try a BEL do so. If not, the Dreadnought I is a spectacular amp for the money.
Cheers,
Michael