Hmmm... My, that raises some questions... First, is it pretty straightforward for you to set up a fixed IP for your printer on whatever router you are using. For years I've had Comcast as an ISP and I used an Apple Airport Extreme and a Motorola Surfboard Cable modem (i.e.., separate router and cable modem). I loved my Apple Router.... Soooooo easy to set up and maintain though not cheap to buy. But recently, for a number of reasons, I am in the process of switching over to Frontier DSL. We recently moved out to the sticks and Frontier is big out in the "sticks" world. They provide local phone and smoking fast DSL with Fiber right to my garage wall. I have only purchased the 30 Mbit/sec package but that is plenty fast enough. I could get 80 (they sell it as 100 but it only does 80) if I wanted to pay more... But Comcast only microwaves a signal out here to the sticks so they have horrible speeds and infamous customer service, thus the reason I am transitioning to Frontier. I actually have both Comcast (Apple/Motorola Surfboard) and the new Frontier system up a running currently. One down side to Frontier is they integrate everything into one "gateway" so I can no longer use my Apple Routers. So I've had to learn how to use the "are you sure you really want to go here and mess with these settings" warnings on the Frontier setup. Like doing Fixed IP and so forth is considered only for those willing to dive in deep to the router. But once you hang around for a while, the settings are pretty easy.
Sorry for the way long aside for getting to the point that I trust you were successful at fixing the IP for your printer. So if you turn your printer on, open Terminal on your Mac and do a simple ping of your fixed IP address, is it there??? You likely know all this stuff but in case you don't,
open Terminal, and at the prompt simply type
ping xxx.xxx.xxx.xxx and hit return where the xxx's are your fixed IP.
If that works you'll get some round trip times printed on each successive attempt. If it fails, you'll get timeout stuff. And <cntl><z> to stop it from just going on and on (and yes, it is control, not option or command).
And when you enter your fixed IP into the printer setup and the Use is not auto-populating, could you try another option I see there called "Select Software". When you choose that, another window opens and I see a remarkably SHORT list of available Printer Software (list makes no sense to me for its brevity) but it DOES contain EPSON WF 600 Series (and a few other Epson drivers). Might that work as something to try??? I mean this is called trying to brute force a set up that works. I can't say why my system auto selects EPSON WF 600 Series the moment I tell it the IP address for that specific printer. But I would think the same would work for you, too... Don't know what's different...
And are you using the MAC address for the printer that couples to whether you are using wireless or Ethernet??? Most hardware I own has separate MAC addresses for those two. I have a note to myself, however, for the Epson WF 600 that says "they appear to both be the same". And the one I used worked so I stopping thinking at that point... But another thing to consider...
And regarding AirPrint, I just did what you said and started to ADD another printer. I clicked on the Default option and got this (see picture assuming it adds correctly).
That's what came up without me typing a word. It auto populated all that you see. And it's this Bonjour connection that is NOT working reliably, what I have moved away from and have now replaced with a Fixed IP setup. So no, I am not seeing anything referencing AirPrint at all. In fact, I've never seen it. I know it exists but that's about all. I just now went and read what Wikipedia says about it so I could educate myself a bit. At first I thought it was for iOS only but I do see that it's also been around for a while on Mac OS X. I just don't use it and therefore no nothing about it. Might I have it turned OFF and am not even aware of how that service got shut down for me??? And I, too, am using Mac OS X 10.10.3.
Not much help likely but that's what I can pass along at this point.
holler back if you want me to try other stuff or whatever...
thanks... bob