krk rokit 5

I'm using my RME ADI-2 DAC FS as the audio output of my Mac (through USB) into a pair of Rokit 5 G3 monitors. In between, I'm using a Mackie Big Knob passive volume control. The problem I'm running into is that at -3.5db output (+13 dbf Auto) on the RME to Big Knob to full power on the monitors...

Please tell me which monitors should I choose KRK 5G5 or KRK 7G5? The main questions are: Does the 7-inch monitor model hiss (make noise) as it was in the KRK 7G4? Is the bass (low frequencies) normal in KRK 5G5? Which ones are better to buy 5 or 7 for a 6x3 room? Will the ADAM T5A/T7A be better...