I remembered that you had raised a similar question here before. That
was late last January from my search of the messages. Buddhaghosa's
Vinaya commentary (Sp I 128) on the phrase "yena Bhagavaa
tenupasa"nkami" may be of some help. It offers two explanations that
can be applied to your sentence as follow:
1) yena and tena are instrumental expressions in the sense of the
locative, equivalent to yattha (where) and tattha (there),
respectively. Then, where those nobles were, there Mahaagovinda
approached.
2) yena and tena are equivalent to yena kaara.nena (for whatever
reason) and tena kaara.nena (for that reason), respectively. Then, for
whatever reason those nobles (are to be approached), for that reason
Mahaagovinda approached.