Head shake is caused by (having owned 2 x 690) - check and fix in this order:
1: steering head - check tightness of nuts (plus lube) and if bearings is worn - as you have a new bike bearings might be out of speck so still check - Also check that triple clamps are in the right position - remember that most bikes come in a box and some assembly is required. The QC is not always what it should be;
2. bike geometry, - caused by suspension - i.e. you weigh 120kg and bike springs is set up for 75kg rider - and then bike front is too light (sag issue) - you must change springs (This can not really be fixed by changing suspension setting). Have somebody like Hilton Hayward (or many other) check your suspension - It is worth every cent - this is the first thing I do with any bike.
- caused by bad design - 690 is an off-road based frame, going fast. but putting in correct springs I have always been able to resolve this issue.
- caused by tyres - tyre sizes changes the geometry and again and can again cause an imbalance resulting in a headshake - I've always used MT21 with no issues, but they might be to aggressive for some. Tyres are like bullets/girls some guns like certain bullets and not others and some guys like certain girls and some bikes like certain tyres;
3. rider induced - if at a certain speed, you hold on to tight on the grips, you pull the front wheel offline, the front wheel wobble, you pull/push (thinking you're correcting the issue but you're not) creating a counter steer which exasperates the head shake. This is resolved by riding more balanced and not riding so tight or with a good scotts steering damper (High speed damping)

I know some people don't like dampers (Not a solution to 1 or 2 - fixed that first) but damper have saved my ass many times racing offroads at high speeds - hitting a rock at 140km is some scary sh1t. Me I put a Scotts steering damper on all my bikes (that doesn't come fitted with a damper).