Empiricism isn't based on eyesight or vision, it's based on what we actually experience. There are ways for us to experience Infra-Red and other spectrum. There is not a real way for us to experience something like "gravitons".
I see from your profile picture that you wear glasses (me too). You're using a scientific "instrument" (your glasses) to view the world. Your experience of the world is modified by those things.
So at what point does a gravity wave telescope depart from the realm of things that we're allowed to use?
Take the example of Infra-Red light. Some time after Sir Isaac Newton figured out that sunlight could be broken up into it's component colors. In 1800, Sir William Hurschel wondered whether any particular color of the sunlight was responsible for it's heat.
So he bought eight identical thermometers and a nice large prism. He broke the light up into the pretty rainbow and put seven of the thermometers so that their bulbs were each lit up by a separate color. Being a good scientist, he understood that he needed a "control" - so he took his eighth thermometer and put it next to the others - outside of the path of light - so he could record the room temperature.
To his horror (I guess) he found that the control thermometer climbed rapidly in temperature - where the ones in the various colors of sunlight didn't.
It looked to him as though the temperature in the room had somehow shot up!
It didn't take him long to realise that there was an extra "invisible" color at the red end of the spectrum...something you couldn't see - but which the prism was separating out just like the other light.
He called that "infra-red"...and understood that by far the most energy in sunlight was coming through the "invisible" parts of it.
So his "observation" used a prism and a bunch of thermometers and produced a result that you can't "directly" experience. Does this count as an "actual experience" - or did his use of intermediaries, such as prisms and thermometers somehow invalidate his experiment in your eyes?
The problem is where you draw the line.
Does the precise measuring equipment used by LIGO to observe gravity waves differ philosphically from thermometers and a prism - or from eye glasses for that matter? Where is the boundary?