My experience with the NuPrime IDA-16 was that it lacked outright resolution and could be a bit lacking in emotion, especially compared to SET based Class A amps so with the STA-9 positioned beneath it according to table provided by NuPrime the observations do make a lot of sense. In the case of the IDA-16 it has been left alone to be as Class D as it can be and as far as that goes it does have some good strengths (bass, macro dynamics, neutral presentation, imaging) and the internal (ESS based) DAC didn't grate as much as I remember the NuPrime DAC-10H DAC/preamp did, though it still sounds a bit sharp. I am a bit mystified with NuPrime's obsession with trying to make their Class D amplifiers to sound warm like valve amps. I think it kind of defeats the purpose of Class D since it doesn't have any of the other virtues of valve based or Class A amplifiers and nullifies some of the typical strengths of Class D amplification (wide category, so that generalisation could be off the mark here), leaving only power efficiency as a plus. I was kind of curious as to how the STA-9 would compare to the other amplifiers tested so far, especially also since it can also be bridged as a 290W mono block so it kind of make sense to get another later so it kind of has a nice upgrade path if you have speakers that require lots of power to sound their best. My recent experiences with efficient systems have been that they are the preferred route when going with 2-channel stereo due to how much possibilities it opens for synergistic systems and enable the use of very high quality low power amplifiers that don't cost a huge sum of money.