A:AnswerThe source of Zone 2 is analog only. You can't use HDMI source to output audio to zone 2. https://usa.denon.com/us/product/hometheater/receivers/avrx1400h
Look under the Multi room/CI section.
A:AnswerMy answer is YES, unless you want to use the speakers in a meeting hall setting. Sadly, I do not know the dBa per watt efficiency of your speakers to give you a solid answer. I drive a pair of Klipschorns with my amp with surround provided by Klipsch RF-7 wall mounted on the sides, the RF-7 center and RF-7 subwoofer. Klipsch speakers are probably more efficient than your JBLs.
A:AnswerI had an Onyko and then a Yamaha but when the HDMI board failed which affected the audio I bought the Denon and I am very pleased. There are not as many built in sound options but it doesn't need them. I have it set up as a 7.1 and the sound is exceptional and I notice an improvement in the video as well. The set up is extremely easy and some features in set up are done automatically for you. I like it.