More importantly, what battery do you have? Specifically, the newer DN110 is what enables synchroshift.

I don’t have the exact answer to your question....

I run almost the same setup but with single button brake levers for caliper brakes. So this should run the same way as you are proposing.

I have my system setup to run the RD from the brake levers; right hand to a harder gear, left hand to an easier gear. I figure if I am standing I would only be shifting the rear derailleur anyway. This was easily setup on my computer using the desktop etube app.

What is synchroshift? One button for downshifting or upshifting?

I liked the look of the double button shifter, and was wondering what happened?

Disregard. Just looked into it. Interesting...I think I'd rather have the older version.

The default will be your old 2-button will behave as they are now, and the new hydro brake levers will shift the RD up and down.

So even if I have the newer battery (need to check), they would behave as you've stated, and they won't automatically shift the front derailleur?

Though maybe I'll just bite the bullet and try synchro with the single button shifters all around....

Assuming you have the newer battery, you customize shift setting using the etube software

If you want front shifting with single buttons, you will need to use the synchro mode. Although with synchro, you can still override the front shifting with a 2 button shifter.

OK so if I understand correctly though...... regardless of how I configure/program this, IF I use the Di2 hydraulic single button brake levers, there is no way for me to manually shift the front derailleur from the base bar?

Yes. It is a little confusing, but the buttons do not affect shift mode. They are independent. The buttons are assigned to a shift action, and that never changes. Separately, you program shift modes (manual, semi-synchro, and synchro). So, you would leave your bike in Manual mode with the new buttons. Or, if you have the ability with the newer battery, you could program a synchro mode and switch to that. And, you can switch in and out of synchro while riding.
Correct.

If you use synchro mode, then front shifting will occur with gear changes automatically.

For example, if you are on the base bars in the big ring as you approach a corner, and start working your way down the gears with the single button. Initially this will be through rear shifts, but when the gearing reaches the predetermined shift point, it will then shift down into the small ring (with a compensating rear shift). As you accelerate out of the corner, and start moving up the gears (again with the single button), you will shift up the cassette until it reaches the shift point, then it will shift back up into the big ring.

With manual or semi-synchro modes, you can't access front shifting with a single button.

OK, sorry, another (hypothetical) question...

If I have an older battery that isn't syncro enabled, and I install all single button shifters......how would the FD ever be shifted?

Etap is starting to sound more and more attractive....lol

Wouldn't it be easier to buy a new battery?

I was kind of getting at - how could I use hydraulics and still be able to manually shift the FD from the base bar.

Yes, it’s possible to control both derailleurs in this situation. You can program different buttons to do what ever you want using the E-TUBE software.

You could set it so that your extension buttons shift the rear derailleur, and the base bar buttons shift the front derailleur. ...not sure that’s an ideal solution, but at least it’s a solution to you hypothetical.