Distortion problem with The Grand via Cubase Artist 8.5

I’m very new to DAWs so please bear with my newbiness.

I’ve just completed my new system - Windows 10, Cubase Artist 8.5 and as a pianist I also purchased The Grand 3. Today I created a new project loaded a new Instrument track, selected The Grand and my favourite Bosendorfer and started playing through headphones attached to my audio interface.

It was truly horrible. Ugly distortions which sounded like overloading on some notes, others were fine. The problem was mainly when playing chords, though some notes caused the problem when played solo. I tried adjusting the various volumes (the channel and main stereo output on Cubase, the volume level in the VST, the volume of Windows itself, and the volume and mix on the audio interface), but nothing made any difference. I tried loading different pianos but they were all the same. I also tried three different headphones - again, all the same (I can’t try the speakers because I’m waiting for my RCA-jack converters to arrive)

Does anyone have any ideas what else I could try? I’m feeling pretty deflated at this point.