I am using S:Flo2 line-out (dual wolfson wm8740 chips) with Sennheiser HD598 & IE80. This is my setup since last 5 years. The FLAC music is good, has mass, good soundstage, good instrument separation. Now I am thinking if I want a HUGE (not just 1 level jump) jump in SQ compared to my existing setup, what should be my upgrade look like & how much minimum do I need to spend? Maybe a new DAC/DAP & HD6xx ? Basis your recommendations, I will decide whether it is worthwhile to spend $$ on upgrade or be content with my existing setup. Thank you.