Remember the old “Yin-Yang” principle which states, “whenever you turn something up, something else disappears. Furthermore; whenever you turn something down, something else gets louder”. This applies to EQ, levels and almost anywhere you have two or more tracks.
You should expect to have different sounding mixes when listening on different systems. They are different systems (different components, different converters etc).
The question is HOW different are they? Are they subtle and only you would notice? Or are they very drastic and preventing you from releasing the song?
The way to counter this phenomenon is to make copious notes while listening to your recording studio mixes. And please remember: your song won’t sound amazing on every system. That’s a part of life. We’re simply trying to hit a high-quality average. We want to make a mix that sounds amazing almost everywhere.
When you feel you have a good mix, burn it to CD and listen to it EVERYWHERE! In the car, in the bath, at home, on the TV set, at your friend’s place etc., and make a lot of notes. If your bass is too loud on System A, too quiet on System B, and perfect on System C: then you’re done! The mix is perfect. But if your bass is too loud on System A, B and C, then it’s back to the drawing board. And at the end, if all your notes cancel out, then you are finished!