Interestingly, the new breed of single driver earsphones, e.g. Klipsch Image and Sleek Audio SA6, are being favourably compared with the top of the range non-custom IEMs, like the Triple.fi 10 Pro.
Some of these reviews and opinions on Head-fi.org make interesting reading:
We've been thinking about offering a service to supply custom fit earphones like the
UE-11 Pro and Sleek Audio Custom, but have been holding back as we are not sure of the demand. It would be interesting to hear some opinions on this.