Lik most I have several pairs of iem and headphones I used my Beats Studio when I picked up the V20 not bad sound not I am giving my Vmoda Zn a shot and will switch to the Shure se 215 later in the week so what r u using.
I am using the standard Samsung earphones for most listening and my wireless Jaybird X2 when at the gym. I have a set of MEE Pinnacle P1 on order to replace the Samsung s, assuming i like their sound profile.
I have been using my Etymotic ER4-S IEMs. Before the V20 I only used them for serious listening with an external amp/DAC because they can be hard to drive. The V20 has been doing a fine job with them. I haven't tried my larger overear headphones with it yet.