I wrote a review for ASR. In short, you should know:
Only one extra Op-Ams comes with the set.
All the extra Op-Amps offered by Aune are no better than a cheap DAC on the market. The sound starts to normalize around OPA627, which can be purchased separately, and because of which you will not be able to close the lid of the device. The optical port does not click into place. The potentiometer has difficulty separating the channels. A POP sound will be heard when laying in/out. Only with Sparkos SS3602 will you have a real benefit. You can initially buy the cheap BB OPA627 and upgrade over time, or upgrade immediately if funds allow and the system is ready for it.