Good headphone sound is certainly a useful reference.
Different headphones/lines still still tend to have different sound and tonal balance as well. So there is no absolute reference even there.
Room acoustics can certainly be a challenge getting a speaker setup to sound like phones. Phones take the room acoustics out of the equation.
With the bottom ported OHMs, floor construction can have a big effect on how bass sounds in particular. More floor interaction with more resonant types of flooring will be harder to get to sound like phones with no room acoustics.
Lots of ways to tweak a setup in a room, especially if many modular treatments are in use. More or less might be better. Other tweaks as well like speaker placement, toe-in/out.
Sounds like one of those situations where you just keep on tweaking towards the reference sound you like best until you zero in on the target.
I have HiFiMAN HE-400 headphones and their EF-5 tube headphone amp and also the KingSound H3 Electrostatic headphones and their M20 OTL tube headphone amp. Both of these setups give great headphone sound.
That said, the headphones. do not compare to the holographic and precise soundstage I get from my Wavetouch Audio Grand Teton speakers driven by a pair of modified Dignity Audio 8-watt 300B amps. The soundstage this develops is mindblowing and very expansive and layered. It's one of those things that you have to hear to believe. The bass is quite impressive too, but if you want "Dance Hall" bass to shake the walls you will probably need to add subwoofers.
I do have acoustic dampening panels in the room as well as a few homemade Helmholz acoustic diffusers (plus a single Michael Green Room tune).
In your particular room, especially if you have the Ohms on the short wall I would guess you'd have all kinds of problems with room reflections because the Ohms dispersion pattern is very wide. And the closer you'd move them to the rear and side walls the worse the imaging would likely be.
To get to a more headphone-like presentation you would need speakers that are more directional... like the Wavetouch, so that the sound is not echoing off of every inch of wall nook and cranny. All that totally messes up the stereo image if it's not well controlled. With the Ohms you might be able to put some sound absorbing materian inside the grills to the outsides and rear of the drivers. That could help a lot.
But if it was me, I'd do what I already did (above) because I know it works like magic.
Good luck to you!
Also, in my large room 14'x30' with high cathedral ceiling (the small room I mentioned above is 11' x 14'), I have the large VMPS RM40 ribbon hybrid monitors powered by a Rogue Audio Medusa amp.
In that room I have a single room-tune in the right corner behind the speaker. The windows have curtains and there are a few sofas around the room. I get very good imagery in this room too with the speakers angled in toward the listening position and using Lyngdorf's RoomPerfect room correction system. The RM40's are somewhat directional too, which helps.
As I said, the imaging is very good in the large room but I think it is actually more enveloping (like headphones) in the smaller room I talked about in my previous post.
Your 5000s have teh 4 3 way level adjustments on each speaker.
Setting room size to small and location to free (for lowest low and mid bass levels) might bring the tonal balance to be more like the Grado phones with less bass. I tend to run my 5s with low bass levels by preference, despite being on solid concrete foundation floor. Too much bass can mask midrange detail and probably be further from the Grado sound.
18" to walls might be a tad close, even with treatments. Of course, if you move them out further, the bass level adjustments on the 5000 can be upped if needed to compensate. Each level on the controls adds/subtracts 3 db to the target frequency range. Very useful for helping adjust to room acoustics and something that cannot be done with most speakers these days.
Tune a quality box guitar to the key of E, tune your system with resonace control useing the box guitar, you would be supprised with the outcome of the sound to becoming shockingly real!, A trade secret revealed by the audiolabyrinth, Enjoy the music.
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.
Also keep in mind that wall treatments affect soundstage and imaging as well. They reduce the levels of reflected sound at the higher frequencies, which is often what is needed to some extent. Lower levels of reflected sound is also what one gets by moving speakers further away from walls, so both can be applied to achieve similar results in regards to soundstage width or depth as needed. However, early reflections are always bad, even at low levels, so some distance between drivers and walls is always a must with any speakers in order to get the best imaging results. Its the imaging and soundstage that makes speakers in a room special. THe rest can be pretty much had for much less with a good set of headphones
Mapman, Sound from each speaker comes to opposite ear with some delay creating image in front instead of the image in the center of the head. Some headphones have acoustic feedback from one cup to another but it can be also done by creating analog delay/crosstalk in the headphone amp or by DSP processing in computer playback.
Headphones eliminate room interactions, but are perceived very differently than speakers or unamplified live performances. Even the rare binaural recordings, though a vast improvement in this regard, don't completely remove this unnatural listening experience. Some processors can help, but I have yet to hear any approach that sounds completely natural. Headphones can be a useful tool to better analyze specific attributes, certainly have their place in certain circumstances, but IME as a holistic listening experience they ultimately fail.
I'm hoping for a pair of phones that might convince me to ditch all the big expensive gear once and for all, but has not happened yet, and I've heard most of the usual top contenders these days plus many a vintage classic along the way.
I have 4 pair currently: STAX, Sennheiser, Klipsch, Audio Technica. All are nice, very detailed, balanced, good dynamics, lots of fun and enjoyable, but can't touch my big rig in terms of sounding real.
How do I know? I can listen for hours on my big rig until I force myself to stop. Headphones fill the bill for awhile but I am always ready to take them off a lot sooner.
Very good for hearing purely what is in any particular recording though. Knowing how different recordings sound in headphones can be a help when it comes time to assess system sound quality because there is so much variability alone just in how various recordings are produced and sound. Think of phones as "monitors". Speakers are needed to communicate the whole deal properly.