we started ours on chick crumb (no ACS as it inhibits growth), went to growers/ rearer (Smallholder so no GM or chemicals) and on to layers when the first hen laid, about 26 weeks. In the meantime the cockerels had been moved to a separate pen and were kept on growers until slaughter at 6 months. Tasted great. We did throw in mixed corn and fruit and greens as well. They were on a grass run, until they destroyed it.
Mistakes we made were slaughtering too late and not employing a 'peacekeeper' with the cockerels. An older bird who assumes top role and stops the others from fighting (which toughens the meat and reduces weight gain). He would be pulled out when they reached 6 months to avoid him being challenged. We slaughtered some at 9 months and they were tough, so tasty curry only. We waited to get the weights up, and lost the quality.
The slower they grow the better the taste. So I guess Hubbards will taste like cardboard always. Ours were Wyandottes and Orpingtons. The skin on a Buff Orpington is too thin to make a good roaster.