Which preposition to use with soloist

in Occurrences 3%

The regular landing-stages were taken by transports, tracks were held for troop-trains, and it was night before we got down to London, where crowds and buses stormed along as usual and barytone soloists in every music-hall were roaring defiance to the Kaiser and reiterating that Britannia ruled the waves.

Which preposition to use with  soloist