Blue,
Here is approach I would recommend to get everything in order.
Good hEadphones like better Grados are a good reference for what is in a recording to hear, ie essentially detail. Each has their own sound though in regards to detail, tonality, distortion at various levels, etc.
I've heard your Grados once recently. My recollection is that they are very revealing through the midrange in particular being just a touch towards the brighter side of many phones, and also very good detail, and smooth.
My OHM 5s, similar to your 5000s are set up to sound quite similar. So it can be done.
The problem is room acoustics. Unlike phones, every room impacts its own sound to some degree. Getting that under control is the first essential.
WIth any speakers, including OHM omnis, getting focused soundstage and imaging is mission one. That requires assessing the room acoustics, liveliness and levels of reflected sound, and then placing speakers and/or treating accordingly.
Large speakers including OHM usually require some distance to walls to achieve best results.
Regarding wall treatments, the same strategy applies to OMNIs as more directional speakers, ie treat primary reflection points first and go from there as/if needed. The difference with omnis is you have to determine where you will be listening from in order to identify primary reflection points, where as with directional speakers there is only a single sweet spot to choose from.
After this, enough space to walls to avoid early reflections is key. I'd shoot or 2-3 feet or perhaps a tad more depending in a room that size.
Then of course, electronics, ICs etc. come into play as well. But you have good stuff, so I woudl not be concerned about that. Focus on optimizing the setup.
If you can do it with the OHMs, you will be in a place that is hard to beat. The key though is to do it. We all know that can take some time, but having a reference sound to shoot for helps. You gotta know the target before you can hit it.
The soundstage and imaging of live speakers is what headphones will never deliver. ITs what makes teh difference between listening to a recording and possibly getting the emotional involvement with the music that one might get at a live event.