The heir 4.Ai would be an upgrade to the SE535. They also sound very similar though. On the other hand, the 5.0 is a completely different sounding iem. I think it would be a good consideration to try out the 5.0. And heir is still going on with their sale right?
I just recently got their rendition 1 on sale and its quite good if you're considering an amp at all
I've never tried any rhapsodio iems before. But all i can say is personally, im quite a fan of the BA and dynamic driver hybrid iems. Ive tried the Tralucent Audio 1plus2 (which apparently has some sort of connection to Rhapsodio?) and i currently own and love the **** out of my ASG-2. Could be an interesting venture to go into too =P