Part of this is explained quite well in Jay Rubin's "Making sense of Japanese".

Kurosawa made the film "七人の侍” (the Seven Samurai) which by virtue of this construction we can recognise as a specific group. He goes on to say if someone killed all seven members of the group, as opposed to killing any seven samurai then he would say:

七人の侍を殺した。

as opposed to:

侍を七人殺した。

when the 七人 operates as an adverb indicating the extent of the killing.

He gives a similar explanation for Old king Cole who called for "his fiddlers three", who were also a group　三人のバイオリン弾き.

(But I'd be grateful if someone would explain how/when one would place を after the counter....as in the examples above.)

Part of this is explained quite well in Jay Rubin's "Making sense of Japanese".

Kurosawa made the film "七人の侍” (the Seven Samurai) which by virtue of this construction we can recognise as a specific group. Rubin explains that if someone killed all seven members of the group, as opposed to killing any seven samurai then he would say:

七人の侍を殺した。

as opposed to:

侍を七人殺した。

when the 七人 operates as an adverb indicating the extent of the killing.

He also gives a similar explanation for Old king Cole who called for "his fiddlers three", who were also a group　三人のバイオリン弾き.

(But I'd be grateful if someone would explain how/when one would place を after the counter....as in the examples above.)