It's silly to charge $128 to make a portable dap work with sensitive iems. Think about it: this (at least the X128 and XD128) is a high-end dap and you have to pay extra to avoid background noise when using sensitive, high-end iems with it. The list Larry provided from Earphone Solutions, which was meant to show some examples of sensitive iems, were all $500+!!! What part of this equation is not farcical? I'll wager that most people who are even aware of it already have sensitive iems to begin with. If anybody should be eating the extra cost, it's those who want to use their full-size cans without an amp (although I suppose they are being targeted with the THD upgrade, as well). It all feels a bit like the showroom of a car dealership.
I wonder what's next...."New perk: for those of you who love classic jazz, we will optimize your Wave to playback classic jazz recordings by blah blah blahing the blah blah blahs. If you like jazz and you don't get this upgrade, it won't sound as good. That'll be $98." I know I'm being cynical - no need to point this out to me in a reply. There may be some very good reasons for their decisions, but I've yet to hear them.
Perhaps this is not the product for you then.
Good reason for their decisions? I'll take a guess that for the base model they want to keep costs down for those who don't want or need any extra features, and they want a base model that works with a wide range of headphones. Now the downside of this is that there may be some noise floor issues for very sensitive IEMs. But addressing this means that the Wave is no longer capable of driving a wider range of headphones as well. What to do? Give an IEM option, and charge for the work it requires. No biggie.