Dear @chungjh : At its prie tag your LA4 solid state preamp is really an achievement and a challenge for almost any preamp out there. Very carefully designed and with high knowledge and skills levels.
"
Benchmark's LA4 is the widest-bandwidth, widest-dynamic-range, lowest-noise, lowest-distortion preamplifier I have encountered.—John Atkinson "
and the unit works in the analog domain.
Take enough play hours with in your system to " understand " the whole improvements and then play again with changes in your seat position and tyny changes in the speaker position. With what you have you need to fine tunning your room/system and then you will know if you need or want to try a " better " cartridge or the like. Enjoy what you have, enjoy MUSIC.
R.