how can I make the back wall transparent?

The only way really is to use speakers that are bi-directional, like Magnepan planars for example, or omnidirectional. Front ported or acoustic suspension speaker designs, ie those where most or all sound is emitted from the front, will be most problematic.

Then it is a matter of getting enough distance between speakers and rear wall for proper timing of spatial queues (usually a few feet minimum) along with a good balance level between the direct and reflected sound that reaches your ears. That is determined mainly by distance from wall and db level of rear emitted sound, ie that reflected off rear wall. More distance to rear wall will require higher db of reflected sound to produce illusion of extending past rear wall. That is why bidirectional or omni speakers tend to do this best.

Again, I think Mapman means "front" wall. I'm in the "room sound" camp (although perhaps alone) where the furniture, rugs, bookcases, me, etc., provide plenty of ambience control. I do have my listening "sweet spot" 4 feet or so from the back wall (behind me...in case we're still not clear on that), and the main speakers about 3 feet from the front wall with a sub tucked behind one of them. Done. The side walls/glass doors are well away from all this and besides, I like some "room sound"...there are bumpy standing waves here and there but not in my listening spot so I don't care. I have a glass coffee table in front of that spot and put a couple of throw pillows on it when doing "active listening" (love that concept), so I'm not a complete philistine.

...by replacing a sheet rock with glass

YEs, I mean wall behind speakers opposite from listening position, which is the one in front of you when listening facing speakers.

You can use room acoustics or fight them. Both are valid approaches. Each might have a better chance of success depending on magnitude and nature of room acoustics. All rooms have a unique sound and best to first assess it then use it and tweak accordingly as needed IMHO.