Xubuntu macbook tincan sound only on speaker

I have read all the snappy posts about tsched=0 fix and solutions like installing alsa again and again.
My configuration is old macbook pro 5,1 and yes I tried installing almost every possible driver like hda-intel. I have also tried the power_save option = 0 and not sure what not

My question is simple,

Why does headphone sounds good on Xubuntu but speaker sounds horrible?? Both use the sound card right. so why headphone is crystal clear sound...but speaker is like a tin can rubbed on a steel road ;)

Any bright ideas except the same old copy/paste ones. Intelligent ideas will help a lot!!!! Plz...pretty please....do think....