As far as I know C5 uses OPA2227 it can be harsh on highs for such dynamic and precise iems like IM02. The harshness is caused due to lack of details on highs in particular op amp. It sounds fine with any headphones except for those with accentuated details on highs, basically IM02 will reveal all deficiency of 2227 op amp which it struggles with on highs. However, in other 99% cases, C5 amp is a solid option. I would recommend Headstage arrow 5 on AD8620, it over kills OPA2227 in everything, specifically in details, and gives a neutral tonality with fast pace, or UHA-6Sii on OPA627 which can make IM02 smoother. Choice of amp for IM02 needs extra attention.