You did very well.
Spend a little and place brass cones and footers under the CD player. Cannot remember if C-350 has pre out/main in. If it does then toss pin connectors and replace with RCA jumpers for BIG improvement.
Don't see Target stand. Should be filled only halfway with sand/shot combination. Too much dampening kills the sound.
Corners need some dampening to kill bass loading and clean up midrange. Listen on.