I had a very specific application for the HA400, and despite the price it serves this purpose very well. My use case was to route my TV to multiple headphones and to a Super T-amp. The main connection is from the headphone out of the TV to the input of the HA400, then each channel of the HA400 goes into a dedicated headphone or the T-Amp. I have headphones with multiple impedance so a simple split cable would not do. The sound quality is quite good, all considered. The HA400 is very quiet until about 85% where a noticeable hiss is introduced in the channel. I A/B compared with few CDs and while there is some sound coloration, I could not feel any meaningful difference between directly playing from a CD player into the T-Amp or going through the TV with the HA400, but of course the whole setup is not for audiophile listening. I don't think this little preamp can really be used for proper headphone mixing, although I don't see a problem in using it for tracking with multiple musicians. This is definitely a well made little box, it does what it says, and is cheap!