As far as the bolt on front mounted spade as one member suggested, it wouldn't last 10 minutes on a larger tractor maybe on a sub compact.
Bucket Spades, like other attachments, come in various builds. Some are pressed steel. In contrast the Bucket Spade from Bucket Solutions is 100 pounds of forged steel. I have been punishing mine for eight years, mostly in tree work and Palmetto removal in Florida sandy loam but occasionally in Lime Rock. A Kubota 'B' is the minimum weight tractor that can insert it and you need moist soil for rapid excavation with a light tractor. On a 'B' one has to be careful not to distort the thin factory Loader bucket with exuberance.
My Kubota L3560 weighs 3,700 pounds bare tractor and has the optional L2296 heavy-duty, round-back bucket. I have unreservedly recommended Bucket Spade for use on tractors with 5,000 pounds bare tractor weight and a Loader, such as the Kubota M5660/M6060/M7060. Tractor weight is much more important factor inserting the Bucket Spade into challenging ground than is Loader hydraulic power.
Your M8540
might be too much.
LA805 FEL weighs 1,279 pounds.
Some of the LA805 weight bears on the BS/BS, say 400 pounds.
LA2296 SSQA H-D, R-B bucket weighs 180 pounds.
Bucket Solutions' Bucket Spade weighs 110 pounds.
So FEL + L2296 + BS/BS total weight = 690 pounds bearing on the sharp 18" edge of the bucket spade.
Once the bucket spade is positioned in the ground, you insert it to depth by moving tractor forward.
Here is a photo of the Bucket Spade on my B3300SU in 2010, planting native hard Pears.