That says more about the reviewers than the products. FiiO themselvs openly tell you the noise floor on the homepage and it is high.Thanks I'll look at more reviews for both.
Too much money, $1200 here for the K9 Pro ESS. From the few reviews I read about those Fiio dac/amps no one really mentioned any hiss with sensitive IEMs, except one with Andros on high gain, what's the noise floor on the Cayin Ru7 that others suggested? It looks quite good at least from the reviews I saw.
Maybe they tested the IEMs on Single Ended? With Analog Amps, you only have half the noise on Single Ended as you use only one amp.
The RU7 is an portable device, its just an dongle and it has pretty bad measurements overall. It has an Channel Separation of 96db on Balanced. There are devices who have better channel separation on 3.5mm. Dynamic Range and SNR is also bad.
The Channel Separation on balanced is almost on the level of my Smartphone.
But it uses an ladder dac with two very cheap amp chips, so that is no surprise. If you put nothing in the device that sounds good, it will not sound good.
Cayin tells nothing about the Noise Floor... you can think for yourself what that means.
The FiiO KA Dongles or the Moondrop Dongles or even the Shanling Dongles are significantly better in everything so i would not recommend it.