It's unusual for a system to throw a deep soundstage. Over the years there have been several attempted enhancements to simulate depth. All of these systems manipulate phase information to trick your brain into perceiving more depth. Here are several examples. You can look up the reviews on this stuff and get a better idea what each option does. Soundstage depth has been a priority for me and I have owned several of these units.
1. Carver Sonic Holograhy C-9. Alters phase information to give the illusion of more depth. I have one and it works reasonably well but you have to carefully set it up and keep your head still when you use it. They come up for sale regularly and are not expensive.
2. BSG QOL Processor. This is the best solution I've found. They are discontinued but ocassionally one comes up for sale. It adds depth and the instruments sit in their own three dimensional space. When audiophiles hear my system with this engaged their jaw drops. I have a spare in case my first unit bites the dust.
3. Baach 3D Spacial Processor. This is the newest gizmo (or software) on the market and its generating lots of press. I haven't heard one but I'm looking forward to auditioning at least the software version. The deluxe hardware unit goes for a heart stopping $54,000. You can get a mac software version for a few grand. Like the Carver, you have to carefully set it up and keep your head in a vice while listening. The ultra fancy version actually has a head tracking function that direct the image at your noggin if you sneeze.
4. Polk SDA Speakers. Polk makes speakers that incorporate phase altering technology to improve the soundstage.
5. Yamaha DSP-1 Processor. This is a different approach in that it has an adjustable delay function for one or two sets of auxillary speakers. It can simulate a live concert to an eerie degree. It takes one or two additional amplifiers and one or two pairs of additional speakers to make it work. I have one but it isn't hooked up at the moment. It's kind of a pain but when you have it running and dialed in it is an incredible experience - especially for live recordings.
There is also an easier experiment you can do which requires a set of bookshelf speakers, stands, and a separate integrated amplifier. Setup the bookshelf speakers back to back with your regular speakers so they are firing at the front wall. Hopefully you have an unused set of preamp outputs that you can hook up to an integrated amp. Hook up the integrated to the bookshelf speakers and experiment with the volume and tone controls. If you have an equalizer hooked into the integrated you are in tall clover. This can add a nice amount of depth to your system.
If you've made it this far you realize that you are not the first person to have this issue. Depth is the holy grail of stereo reproduction and there has been a lot of attempts to solve the problem.
For the record, I'm running a pair of Thiel CS6 speakers with a Krell KSA 300S amp. The speakers are 6' from the front wall which is the best place to get maximum depth without any processing. With the BSG QOL I have a window that sounds like a deep soundstage with instruments that are placed left to right and front to back. It's pretty amazing.