Upgrade advice needed

Hello,
I currently have a modest, entry-level system consisting of a Marantz 4500 receiver with Paradigm Mini Monitors, a PDR-10 sub and Atoms as surrounds.

I use this system 80% for 2 channel music (2.1 technically). Though I don't use the surround as much, I definitely like/need the option enough not to be dedicated only to 2 channel.

I would like to upgrade the mini monitors, possibly to Studio 20s or comparable. Will the Marantz hold up to the next level in speakers?

I realize the next incremental step would be to add a 2 channel amp, possibly using the Marantz as a pre-amp.

But what do you think? Can I make a speaker upgrade with what I have? Is the right direction to go? I would appreciate any advice or suggestions on how to take the next step up.

Thanks
Tim