Fred,

My cheap Denon isn't rated for 4 Ohms either but I've tried blowing the damned thing up a few times by playing it loud into the 80s and it won't quit. It doesn't even get hot.Even when they are set to large.

Now your Yammie may get hot if you push it which I doubt you will unless you have hearing disabilities. Heat reduces the lifetime of your components. By how much I can't tell you unless you contract me to develop an MTBF model for your Yammie. PM me if you are interested in a quote for this service \:\) .

House of the Rising Sone
Out in the mid or far field
Dedicated mid-woofers are over-rated