Is it obligatory for one who prayed the Zuhrayn prayers with jam' taqdim (combining and advancing) to pray the Ishayn prayers with jam' taqdim, or is he given the choice between advancing and delaying?

If the questioner means combining prayers during travel, then it is permissible for the traveler to combine two prayers (Dhuhr with Asr, and Maghrib with Isha) either by combining them earlier (Jam' Taqdīm) or by delaying them (Jam' Ta'khīr).

So, if the sun sets while he is dismounted and intends to depart, he combines Isha with Maghrib as Jam' Taqdīm. But if the sun sets upon him while he is in motion, he delays Maghrib until the time of Isha and prays them both as Jam' Ta'khīr. Similarly, for Dhuhr, if the sun passes its zenith while he is dismounted and intends to depart, he combines Asr with Dhuhr as Jam' Taqdīm. But if the sun passes its zenith upon him while he is in motion, he delays Dhuhr until the time of Asr and prays them both as Jam' Ta'khīr.

This is the Sunnah of combining prayers, and combining is a concession to facilitate for the traveler while ensuring that the prayer occurs within its prescribed time or the time of its paired prayer.