"In either case, you can ask JPM to do a rollover from the JPM IRA to the new 401k"
If the JPM account is a Roth IRA, rollover to the new 401(k) is not permitted. A rollover of a Roth IRA can only be to another Roth IRA. Further, after-tax funds in any kind of IRA are never permitted to be rolled over to a 401(k). Even if these types of rollovers to a 401(k) were permitted, it would almost never make sense to do so.
