I have two SCR-8 Realistic boomboxes, but I'm not impressed with the amp output on them. I've replaced the woofers in one of them with some newer long-throw 4 ohm speakers and still too much mid range! I know the original speakers are 3.2 ohm, but the 4 ohm shouldn't be too hard on it. I guess that's just the way these boxes are EQ'd. They're very LOUD though! I would just like it to have more bass and less mid at low volume.
Mine sounds pretty even with a nice light rumble for its size. I've always believed that boxes age differently depending on their life use, environment and service history.
Could it be just resistors, and caps in the preamp going bad with age, causing it to sound bland? I know nothing about amplifier repair, but would sure like to get them to sound better.
The Stereo Wide is not good on these Funai boxes, they didn't calibrate it very well. As to why yours doesn't make enough bass, what other boxes are you comparing it to? Mine makes plenty of bass, just like the GE Blockbuster. But they only have 5 watts per channel, so you can't expect M70 level sound from them. Also everyone's is going to sound different due to its capacitor age/condition.
Sometimes I'll AUX in some heavy bass music, usually Beastie Boys, and see if I can squeeze a little more range out. Once the speakers go under 6" they really struggle to get any low range sonics.