[Q] Unlocked bootloader, flashed Philz, rooted, s-off... Now how do I update?
Answer: You don't.
My opinion, official OTAs have no place on modded phones. You went through all the effort to enable your phone to flash custom ROMs. So the last thing you want is to install an OTA. If you want OTA, you need to go back to stock recovery. Its a big step backwards, and completely unnecessary.
The features you mentioned can all be applied without OTA. You can just flash a stock rooted version of the 1.58 ROM; or flash a custom ROM based on 1.58. Better yet, flash a custom ROM based on the (non-AT&T) "international" base as IMO they are much better than the bloated, gimped up junk AT&T gives you. In fact, Extreme Power Savings mode was available on the international ROMs a good while before the AT&T OTA started rolling out.
For a new radio, since you are S-off, just go to the radio thread, and download and flash the new radio.
This is the type of thing you did all this for (unlock the bootloader, root, S-off), is it not?
Everything mentioned above can be found on my Index thread: http://forum.xda-developers.com/show....php?t=2751432
Also, using Titanium Backup, I don't see how it could have taken "several hours" to setup the phone again. Get the paid key (which enables batch functions) if you haven't already - highly recommended if you will be flashing ROMs with any frequency. Using batch backup and restore, it should take about 5 minutes to restore you apps and app data. Then a little while longer to manually configure settings, home screens, etc. I am up and running after flashing a new ROM in 20-30 minutes. Maybe a bit longer if you have a lot of very specific settings. But we're still talking maybe an hour, tops.
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Phone: AT&T HTC One (M8)
Tablet: Samsung Galaxy Tab Pro 8.4 (WiFi only)