Wow, I just logged back on and saw so many replies!
I will measure the impedance of the drivers this weekend, to make sure they all seem normal. I can also rebuild the crossovers, as at least swap out the caps, once I find what the correct values are.
I have tried playing with distance from the wall and corner. I can get a warmer sound by going closer to the corners, at the cost of losing bass definition. I have placed the speakers where I have a good blend of bass warmth and definition, but still have trouble with the sizzle.
Regarding front end components, I've been a long time audio nut and more recently have been building some PASS DIY projects, so I have a few things to choose from: DIY First Watt M2, DIY Pass B1 buffer, DIY Amp Camp Amp 1.6 monos, and I am about done with a First Watt Aleph J. I also have a pair of Quicksilver tube amps. The KG-4 sounds amazing via the M2, but so far I think the Forte does best with the ACA 1.6. I use a good R2R DAC in front of everything else.
Japosey and Shakeydeal mentioned the squawker and horn as being possibly responsible for what I am hearing. Is there any smoother options available if it turns out that nothing else alleviates the problem?
Once again, thanks for all of your thoughts,
Alan