A deeper more holographic soundstage.

Interconnect and cables CANNOT make a big difference only a small one...

You cannot compare one second the combine audible effects of the decrease of the noise floor of the house and the controls of vibrations, and all the acoustical tratment and controls with the purchase of few cables, so good they could be....

It is not necessary most of the times to invest money....Just think, listen and experiment with cheap materials and very low cost electronic device... ( my schuman generators for example cost 10 bucks my grid of 12 cost a little more than peanuts then)...

I use aluminum paper with many other cheap materials for my room....
Cost 3 peanuts?
I created a polygonal shape (rectangle+triangle) with rigid and dense cardboard +aluminium paper covering it, to transform the void corners of the ceiling in polyedral convex flowing shape... The waves love that says my ears to my brain... This is only an example of how we can make the room an able tool ...

Audio forums are all about buying and buying.... I am more about listening/ thinking and listening....😊

Everything is dependent on everything else. You have been given some very good information on speaker placement, toe-in, room treatments, etc but the truth is some speakers and some electronics do not do a very good job of recreating depth no matter what you do. Generally, tube gear will work better than solid state for depth, but again that's a generalization and some tube gear is better at this than others. Removing componentry from between the speakers may help or may not, depending upon the speakers employed. I have heard speakers produce depth in this configuration and have heard others produce little depth with nothing between them. Experiment with pulling your speakers farther out into the room. You may lose bass reinforcement, but sometimes you have to choose what's more important to you. Good luck and have fun with it.

A good tube preamp will tend to give a much deeper and more room-filling soundstage if the rest of the system is up to it.And yes with a SS power amp.I have heard that effect many times in many systems.Supratek preamps are especially good in that regard and why so many people use them with SS power amps.Especially the DHT ones.Once you hear that there is no going back to flat and congested sounding preamps.

How so and at what cost i.e. what did you give up/lose.

Suspect the OP is thoroughly confused at this point.