quamquam est in Originibus solitos esse in epulis canere convivas ad tibicinem de clarorum hominum virtutibus;
This est is followed by Acc and inf as if it were an oratio obliqua. It seems as if it were like est ut, this is at least what OLD SAYS. Gildersleeve and the other grammars I know do not mention this construction. So, could we say instead: quamquam est in Originibus ut soliti erant in epulis canere convivae…? I am not sure…
ok this est stands for ‘scriptum est’ with acc and inf.
est with ut takes final clauses sequence with subj unless in Plautus.