You're going to struggle. Your Rokits are powered studio monitors designed to be connected to either a mixer or to an audio interface with a volume control and a dedicated pair of outputs for powered monitors. Your Yamaha amp is a regular integrated amp designed to be connected to a passive pair of speakers, not powered monitors. It's apples and oranges. The amp does have line outputs on the back but they aren't linked to the volume control as far as I can tell by looking at the manual, so if you plug your Rokits into them you'll either get low volume or they'll blow your eardrums out, depending on what strength of signal the speakers expect to see at their inputs. At a push I guess you could rig the speakers to the amp's headphone output with some mockup of a stereo 1/4" jack at the amp end going to two mono 1/4" jacks at the speakers end, but even that's a bit 'laccy-band and duct-tape'; really your amp and speakers are just not designed to work together. Who told you to buy them?