Well I am no so sure that is a good question. When you listen to the STX, you are listening to the dac and amp (or at least I am since I need the amp for my headphones). So when I listened to the modi, it was with the magni. Was the modi and magni better than the STX? Ehhhh marginal really. But do I know what the modi sounds like? No. There is not a good way for me to judge it against the STX.
Honestly, the the modi and magni are better, but I don't think you would get your moneys worth after listening to the STX for any length of time. To get any sort of a wow factor, you need to save up your money for a better amp, and use the STX as a dac. Later on down the road, get a better dac.