No, the MX-500 doesn't have state memory like the Harmonies, so would turn off the TV if your macro was using a power toggle command. You should get around that by using discrete power codes ("power on", which leaves set on if already on, rather than "power toggle"); you'd probably need a cheap OneForAll remote to get these programmed into the MX500. If you don't want to put in the effort to find the discrete power codes, or if your equipment doesn't have them, you'd have to use a different macro strategy. Like having a power on macro toggling everything on, power off toggling everything off, and the device macros being used for input switching only without using power commands.

In my view the 676 is better featurewise, but the MX-500 is better ergonomically, with better button size, feel, spacing, and placement. I've been using an MX500 for almost 5 years, I have discretes for almost everything so it works great, Harmony wouldn't be any easier for my system.