I've had flower beetles such as Cotinis lay in topsoil as well as Granti but they didn't lay a large amount. So some beetles will lay in non flake soil but you tend to have better results using flake soil in my experience. Secondly Xyloryctes appear to be a hard genus to get to lay with not many...
Selling a Spiropoeus Fischeri for $100 It’s ~5.5” adult male with injured gonopods. Pickup preferable in SoCal dm me for city. No lag available if shipped. USA only.