Options for Fixing "Buckling" Implants Above the Muscle?

Of course without seeing you in person, I can only offer general advice. The first thought that comes to mind is coverage; implants above the muscle will usually show more of whatever is going on with the implants, whether it is buckling or rippling. So going under could help but there are other issues with that for an athletic person, such as dynamic breast which is distortion related to muscle activity.
The second thing is size; in the 600 cc range, there will be more of a tendency for what are called traction ripples, which may be a contributing factor. The related choice of profile type is a bit tricky though; it relates to the volume of the implant and the base diameter of your breast. I presume that your surgeon chose high profile because that was the best fit for a 600 cc implant on your breast's base diameter. If that is the case, low profile just isn't an option unless you go quite a bit smaller.
If you keep the same implants, above the muscle but try to correct it by expanding the pocket, there is the risk that the pocket will thin out more and you would paradoxically see even more rippling or buckling. In cases like yours I have most often recommended a partial submuscular respositioning using a split muscle technique so that there is no problem with muscle flexion deformity but good upper coverage. That helps to smooth the transition and correct the shelf. The pocket dimensions could be adjusted as well.

I am not sure what "buckling" means. If you mean palpability or visualization of the implant, then you probably need more soft tissue coverage and perhaps under the muscle would be best.

Rarely does a patient get everything for nothing. That is, there are imperfections of the implant procedures that you will need to accept and reconcile this with want will make you happy. Since I do not have the advantage of examining you, I can only interpolate from what you have said so far.
It sounds as if your breast soft tissue have been stretched either preo-op or from the large implants that removing them will produce a saggy appearance, hence the suggestion of a lift if you shifted the implants to a submuscular position.
The texturization of the implants, especially on top of the muscle in someone who might have somewhat thin tissues to begin with will be prone to rippling and wrinkling and possible visible folds even if the pocket is made larger.
The pockets will ideally be only as large as the implant because the purpose of the texturization is to allow the soft tissues to stick to the implant surface. The shelf-like appearance is probably due the high profile nature of the implants and the size relative to your native breast.
If you want to get rid of visible folds, you should consider a smooth implant and/or submuscular placement. if you have a saline implant, consider switching to a silicone. If you like the size and shape of your breasts, then you might not want to go submuscular.
I am not sure what the motivation was to use textured implants. Perhaps it was the fear of getting a capsular contracture in the subglandular position with a silicone implant. I usually start with the smallest, lowest profile, round, smooth implant that fits the anatomical dimensions of your native breast and if this doesn't get you what you want, you can vary the dimensions and location of the implant.
Most patients will opt for submuscular because it allows for less risk of capsular contracture and better mammograms and less long-term soft tissue atrophy. There is no best procedure, only choices determined by the priority of your desires and assumption of risks.