You are right, there is a huge differnce between internal piezo mic and external good quality mic with good amp.
I use MXL V87 mic with PRESONUS TubePre tube amp. The amp is very low noise (I tried a bunch of other amps, this is the lowest noise I could find among medium-priced amps).
Paulino Bernabe 'India' 2001
Takamine C136S 1976
Masaru Kohno No.6 1967