Warning: Le Cimetiere Des Arlequins has horrible sound - which is odd, because to my ears both Caricatures and Au-delà du Délire sound great.
I agree that the first 6 are good to explore. This is how I rate them:
Caricatures - 4 stars
Le Cimetiere Des Arlequins - 3 stars
Au-delà du Délire - 5 stars, and in my opinion one of the rare albums that blows away the PA scale.
Emile Jacotey - 3 stars
Par Les Fils du Mandrin - 3 stars
Guet-Apens - 4 stars
After this, I would recommend a different approach: skip to Les Larmes du Dalai Lama and follow up from there - in my opinion, Le bois travaille, même le Dimanche is their best since Guet-Apens.
Also, if you enjoy their later albums (and some are indeed quite enjoyable, despite less progish), you must get the brilliant Troisieme Étoile A Gauche (it's under Christian Decamps, but it is really the current line-up of Ange).