I don't know if the op will return, sometimes new posters are one and done on forums, but I hope he or she does because it's a great question. I've been thinking about this for bit and I have arguments on both sides. The IDA 8 has a lower price, you get an up to date dac, a phono stage, and a nice amp. The ST 10 gets you a much nicer amp, and the argument that you should always buy the best component you can afford, kinda like picking the best athlete instead of for needs. And I know you specifically said these were the options you were considering, but I have to say that the DAC 9 and STA 9 is very attractive because it answers the above conundrum quite nicely. You get an up to date dac, and a nicer amp. The rub is that you have to want a warm sounding system. If not then it depends on how much you like the Zdac. If you're happy with it then the ST 10 for sure. If you're looking to upgrade your dac, then of course the IDA 8 is the next best choice, albeit a little warm too.