This is not a problem with the machine itself (assuming its all working properly) it must be something you are doing, wrongly. There is no way the Vf160 is a 'tinny' recorder, it just records flat whatever you put into it.
Yep your monitoring, or your PC setup is at fault, or it could be the way you are exporting to PC.
Instead of playing the stuff on PC make an audio CD and play on various people#s hifi systems, in the car, boom box, etc. See how that sounds. if that sounds OK then its your PC setup or the way you are exporting to PC, if it sounds tinny on all the hifi systems then look to your mixing technique and monitor setup.
I have never heard others complain that the vf160 sounds tinny.