Ya believe it or not you would have to spend much much more to get an upgraded sound to the isurus. The Soundmagic PL30 will not have the detail of the Isurus but will not have the highs of them either.. I am used to sharper high tones these earphones make but I also own the upgrades in this sound signature and have been listening to those.. The ATH-CKM77 and ATH-CKM99.
For the price the Soundmagics are solid earphones minus the sharp highs. You thought about getting one the Philips SHE3580? Those are bassier and have a smooth sound to them and are cheap too. No different tips needed.