[bugsy]

Hello people!
I bought a China-made acoustic-electric guitar fashioned after the Martin D45.

Now, before you start shaking your heads in pity for me, hear me out. The guitar isn't all that bad: solid top, rosewood veneer back and sides and REAL abalone binding front, back and sides.
It sounded great and I put medium strings on it and it sounded greater (at least to my ears).
It had a bone nut and saddle, but somewhere along the line, I learned that a TUSQ saddle and nut help accentuate whatever properties the guitar has. So, I changed my saddle and nut to TUSQ, and there began my problems.
* The guitar refuses to stay in tune
* All the strings buzz from the 5th fret up until the 13th fret

I might add that the neck cannot be loosened any more, and I have found some uneven frets which I have tried to level (lightly though) and crown.

Any help, explanations, advice will be greatly appreciated.