Anyone using MM7055 with 4 ohm Speakers?

I agree with Mechans, ignoring a manufacturer's guideline is just asking for trouble. Speaker/amp matching is extremely important. A 4 ohm speaker is more demanding on the amp, causing more current draw resulting in more heat. Think of it as connecting two 8 ohm speakers to the same channel, a parallel connection. Take a look here,

http://www.mikelights.com/speaker1.html

In addition to the impedance issue, the MM7055 is just a baby step up, if that, from your SR7007, as I answered in your other thread about the MM7055.

Also, sorry to say that your receiver, the SR7007, has the same impedance issue. Looking at the back of the receiver here,

http://us.marantz.com/us/Products/Pages/ZoomImage.aspx?img=/Assets/images/products/SR7007/XL_c26-MARSR7007-bk.jpg

it states speaker impedance, 6-8 ohms. Using 4 ohm speakers may work OK for a while, but eventually will result in premature failure.

Looks like the simplest solution to your problem is to get a stereo amp that is rated for 4 ohms to use with the RX8s, and run the rest of the speakers on the SR7007.

Again, ignoring the manufacturer in the proper use of their product will just result in a bigger problem later.

I once ignored a warning from Marantz and lit my amp up in flames. I would take their advice seriously.