I own one of each. I first bought an RF-7 II for a mono system for my basement. Later I bought an RF-7 for a mono system for use on my sun porch during the summer. My neighbor complained about me listening to music on my porch, so I moved the RF-7 to the basement, and I'm now running stereo: RF-7 II on the left channel, RF-7 on the right channel.
I don't notice any difference between the sound quality of the RF-7 and the RF-7 II. The differences that are apparent: The RF-7 II is larger, has a different style grill, and seems to be slightly less efficient. (When I use a stereo amp to drive these speakers, I have to swing the balance control to send slightly more power to the RF-7 II.)