I feel it's very tricky to find something that is a direct upgrade to the Prestige LTD that's won't cost double or tripple the price. You can maybe find something that has more detail, bass slam, soundstage etc. But to be completely a full upgrade that has better low end, better mids, better treble, better staging, better imaging, better tuning etc..... Goodluck. I'd stick with the Prestige LTD, and look for something different. Something that compliments the Prestige LTD. I'm currently looking at the Symphonium Titan as a basshead iem or maybe I'd go for the Symphonium Crimson. But most likely the Titan would be my pick.
There also is the Fatfreq Scarlet mini that has insane amounts of low end and good technicalities for less. But also the Fatfreq Maestro which could be another bassy set costing a lil more. The Prestige LTD is a great all rounder iem. But now, I want something for my bassy needs. And also something that's more in your face and hyper detailed.