All X9’s currently come fitted with Michelin Gold Standard tyres as original fitment. Older models had Pirelli or Dunlops, both of which proved less satisfactory.
Some Pirelli tyres suffered delamination across the tread grooves, notably on the front tyre, and also wore on the shoulders giving a very unstable sensation when cornering.
The Gold Standards give long life and very predictable handling, but to some riders, they are a bit bland, masking some of the feedback required for brisk riding. Their stablemate the Michelin Pilot Sport seems better suited to the sportier rider, giving more lean angle for a given speed and yet retaining the same level of grip, wet performance and mileage. Bridgestone Battlax as used on the Nexus add quite a bit of sportyness to an X9 too.
Gold Standards can sometimes be hard to source so don’t leave it too long before ordering a set.
 

Brakes are best left as standard.  No one as yet has found any pads or caliper upgrades which are worth the extra cost or effort, and the standard pads cost less from a dealer than most of the aftermarket alternatives.
One item which needs regular maintenance is the caliper mounting bolts and also particularly on the front calipers on 250 Evo models, the pad retaining allen head pins which can sieze. A smear of copperslip on them occasionally helps prevent this.
The X9’s brakes are linked so the left lever provides full braking to the rear wheel and a pressure limited amount to the RH front disc, for safe braking in corners or on slippery surfaces without the normal ‘sitting up’ or the loss of overall braking by not using any front brake in those circumstances. The front brake is normal on th LH front disc.