An Arcam and yer Diamonds will make some nice sounds together imo.
Not heard the latest FMJ ints but could have a meeting with the A38 if chances coincide. A Wam VIP just bought himself some Faithful Musical Joy and he's hypnotized me a little. ("no, I still want Naim!")
One thing that's outstanding about the Arcam amp sound is the tidiness. When I bought some Castle speakers yonks ago, they were demoed with a A85 using Sheryl Crow's Live in Central Park. I never forgot the presentation of the drumming; the complex textures of the sounds from the stick hitting the drum-kit were fully realized without any splashiness or smearing. Deft, textured and taut! Since then I have not heard another brand achieve the same feat. If your tastes lean towards pop band music, a FMJ could rock your world. Having owned past budget Marantzes and Rotels, I'll venture that the FMJ trick with drumming is outside their areas of expertise, so the PM6003 is unlikely to match the A18's ability to capture textural complexities.
Good luck with the auditioning. Like good ol' G I'm interested to hear your findings.