You can get great results going down this path. However, it's expensive and complicated...
I would invest in a calibrated mic with the OmniMic system or REW, it's really easy to use and understand and will point you in the right direction. Then, get a 2x4 DSP system, just a basic one to experiment with crossover slope and frequency.
For starting points, if you can get a sub right next to each speaker, firing forward and in stereo you can probably push the crossover frequency up to around 150 Hz (depending on the sub, some won't sound good up that high), which will really fill out the impact and energy in the low end. Start with a 1st order crossover on the Omegas and see if that's enough so you avoid excessive excursion at the volumes you'll be listening. Bass is usually better crossed over steeper, like 24 dB. But with DSP you can dial it in to your gear and preferences.
The biggest issue with this is the large amount of capacitance you need for the high pass filter on the Omegas. To not significantly degrade the sound you'll want to use something like Clarity ESA 250V caps with a Jupiter copper foil bypass cap. This will cost hundreds of dollars, and is why you need to measure and experiment before putting the cash down. There are other ways to skin the cat, like a very high rez DSP system, I have a 32/384 unit, but it's not going to be any less expensive than a pile of film caps.
I think for bass you can use the DSP for xo or get a Crown amp with built-in DSP... I'd avoid plate amps. And for the sub go with one that has a driver that sounds ok at higher frequencies. Louis might be able to make front-firing 8s, also AudioKenisis might have a good solution... Maybe get 4 and flank each speaker...
While this is more hassle the results will be much better
than a traditional sub xo'ed around 50-60 Hz and running the mains full range. The Omegas will be able to play at SPLs you never thought possible, and you'll get the impact/energy in the 50-150 Hz range far better. It can be done seamlessly but might not be easy or inexpensive.
I've heard a lot of tweeters and the Fostex T500AMkII are the ones to get imo, put them on top of the speaker aimed right at the LP. Only a small cap required for xo... I'm using .57 uF right now. Basically, I'm attenuating a higher efficiency tweeter by raising the xo point instead of using resistors. For this, it works perfectly. Lower end tweeters might not be worthwhile... yes the tweeters cost as much as the speakers, but they are totally transparent and blend with the RS5 drivers perfectly.