Perhaps you should contact Paul Speltz regarding the autoformers before you make any big steps. I have not tried these, but I believe the purpose of them is related to your issues. Based on my assumption that the impedance curve of your speakers combined with their sensitivity and amps' dampening is creating the problem. I don't own or use the autoformers or zeroformers, but I think this is what they are supposed to address.
Do subwoofers really help?
Easy question here all...if you mismatched your amp and speakers (meaning your amp has trouble with the load of the speaker), do Subwoofers really fix that problem? Is it smarter just to sell your speakers and get ones that better match the amp?