Kept as in still own but not sold (yet) ?
kept as in stored but not used ?
kept as in 'collection that is hard to part with' ?
kept as in used most often ?
Used most often: HD800 (with non Harman EQ), DT1350 (portable duty with EQ) and recently for closed usage (max a few hours) modified Creative Aurvana Live! 2.
Used now and then depending on mood and need:, modified/filtered DT770, filtered DT1990, modified S4X Reference 1.1, filtered HD560S
Kept (hard to part with): HD650, HD58X (modified, filtered), HD681 (modified, filtered), Edition XX, Audeze Sine (modified, filtered), HE35X(modified, filtered), old DT990(600) and a few prototype headphones.
Have not sold (yet)
Why ? Because I either like the sound + comfort or they have some kind of 'sentimental value' to me or have not put them up for sale (yet)