I think you are over analyzing this too much because I am pretty sure, if you stay on this board, you'll be trading your desktop amp/DAC in a not so distant future unless you're the type of person who can stop soon after that purchase. If you are that kind of person then I would understand your hesitation. I find the best way to approach a purchase and that's just my opinion is to make a list of the features you want in a desktop amp/DAC including the price. You do have to be reasonable. Then mark the list if you hit the features and buy, else pass. If you can't stop at buying a unit then just pick any, you'll sure trade it quickly down the road. If you do get a draw then flip a coin.
If it's features, the iDSD has the m9xx pretty much licked. But my decision is more practical. I can't get the darn thing for less than 500 over here.