After some teething problems with the set-up, I finally completed setting up the Asus RT-AC68U to replace my RT-N66U. I had to yank out all the other network cables and just have one network cable from the iMac to the Asus RT-AC68U for the initial web GUI to show up properly.
So far so good.
Wired network transfers, from NAS to NAS and PC to PC, are faster. Wifi range is a tad better than the previous RT-N66U, though I am still using Asus EA-N66 "Spaceship" as a 5GHz wifi access point in my furthest room for 5-bar speed in that room.
Port forwarding also ensured that the uTorrent works at top speed.
The SONOS is working properly, none of the problems I have read about the RT-AC68U having issues with SONOS. It may be because of the updated firmware. Apple TVs working. Netflix also ok, with the Unotelly DNS settings inserted. FTP also set up and working.
A firmware update also made the RT-AC68U capable of supporting HFS+ drives for Time Machine network backup. Gonna hook up a USB3 drive to this and test it out. The RT-AC68U has both a USB3 and a USB2 port. My previous RT-N66U had two USB2 ports only. I expect to see further speed improvements with a USB3 drive connected to the new router.
By the way, if you are having problems with your iPad not being able to connect on the 5GHz wifi, try setting the 5GHz to a fixed channel rather than to Auto. Try both a low-numbered channel and a high-numbered channel. I am on channel 36.
Next up, bring home the MacBook Pro retina from the office to test the 802.11AC wifi speeds.