Let's not forget the AK240 also has...
1. Built-in 256GB memory which is like $400
2. USB DAC. The Hm901 requires a converter or the upcoming dock which is another $300-400
3. Native DSD support
4. Balanced line-out (with an optional adapter, I think). The 901 doesn't have this option (yet)
5. Wireless streaming
1. Welcome to 2013, 256GB of NAND flash hasn't been $400 for several years. It's more like $100, tops and retail price at that. OEM cost is cheaper. Unless the AK240 has SLC memory like an SSD.
2. USB DAC, yes. HM-901 does not have this function built in. Major oversight IMO.
3. HM-901 also has DSD support.
4. Both have Balanced Headphone outs, neither has true Balanced Line Outs at the moment. Maybe that will change.
5. Sounds interesting, but if I'm going to tether to music on a server, I'd rather just run it as a DAC and use better software like Foobar. But either way, the AK240 wins on both counts as it supports USB DAC internally.
In the end, the $2500 cost (and polarizing industrial design) is the AK240's major downside. I find it difficult to find the value there. Other than extreme mark up in price, even if the AK240 were actually made of solid milled titanium alloy, it's still vastly overpriced, there's no arguing that one. And the UI is just built up on Android, wasn't developed from scratch. But the UI is done right, unlike the HM-901 which is also built up on Android, but is quite terrible. But extreme mark up in price is quite common in the "audiophile" world. But just because something costs more does not always make it better.
I, personally like a product artificially more premium by just having a higher price tag, but iRiver can charge whatever it wants. They obviously want a smaller market and to keep the AK240 "special". Which is fine. But in the end, it's all about sound quality, and the AK240, unfortunately falls a bit short. And for $2500, it shouldn't have any compromises, especially in the sound quality department. It's a lot cheaper to compromise on sound quality and have convenience, which is why Apple dominates the market.
The upcoming Calyx M is more of a real contender for the AK240. It has the potential to be superior. The UI also borrows from standard Android UI (rather than throwing them out the window like the HM-901). The ESS Sabre chipset has the potential to have noticeably better sound quality as well, but how well it's implemented will remain to be heard. The industrial design is much more restrained and classic, and looks to be much more pocket friendly, let alone comfortable to hold in a right hand. But it's vaporware right now, and iRiver has already delivered a real product.