What level was the schwannoma at and on what side? Did the symptoms you currently have start two years after the schwannoma removal or did they start immediately after the removal?
The symptoms you currently have (“I feel as if I am walking on glass, I am lucky if I get two hours of sleep a night, bizzare electrical sensations, pulsating pains, etc”) are generally not radiculopathic (related to nerve root compression). Nerve compression pain includes pins and needles, numbness, pain and ache along a specific pattern (dermatome).
However, you do have probable compression of the L5 nerve roots by report; (“I also have a separate issue of L5-S1 anterolisthesis w/moderate bilateral neural foraminal narrowing”). Look at the section regarding “Symptoms of lumbar nerve injuries” to see if any of your current symptoms fit with an L5 nerve injury.
You can use epidurals and selective nerve root blocks to help determine the origin of your symptoms. See those sections and “pain diary” to understand the concepts of using nerve blocks for diagnosis. If the symptoms are generated by the isthmic spondylolisthesis at L5-S1, you can have that level surgically addressed. If these symptoms are generated by the old schwannoma site, a spinal cord stimulator (see website) can be helpful.