Haha, I do not know if I am a modifying machine but I like to tinker!
Here are the new speakers I added. The 28RLPR only has speakers "A" which are inside, and speakers "C" which are the exterior pair. I added a second set inside which are now speakers "B". I placed them in the entertainment center and they are completely removeable, you would never know that they were there if I take them out in the future. They sound great.
The speakers cost me about 25.00 for the pair and the speaker grill cloth cost me 12.00. I made 2 speaker boxes out of scrap plywood and mounted the speakers in them. I then connected the speaker wire to the "B" output on the back of the stereo. I then made a small frame out of scrap wood and stapled the speaker grill cloth to it. My last step will be to use sticky velcro to hold the grills in place. Here in the pics they are just sitting inside the opening.
Before:
Speakers in place:
After with the grills. I bought beige speaker grill cloth to blend in with the interior: