Jolida Foz SS-X Tube buffer & soundstage expander?

It doesn't. The Loki has 4 bands for tone control. The Foz only one (bass). The Foz has a phase control which can affect the soundstage quite a bit. The Loki does not. The Foz has a tube buffer, the Loki does not. The Foz adds a bit of warmth to the overall tone (great if you want it). The Loki is fairly neutral when bypassed. The only thing that is duplicated is the bass tone control. 

I just bought one of these for the fun involved in playing something different. I’ve always wondered about the effect of adding more out of phase sound to the front speakers. Now I know. In small doses it can definitely be additive.

I have a fairly well set up system with an excellent soundstage considering the size of my room (13x19x9). Very good pin point imaging and detail. Added to my system between my sources and integrated amp - Bass control warms up the bass a tad but it is not a huge boost in the upper bass as so many are. It is also effective in toning down the bass from some sources (my Marantz CDP for example). It’s effect on sound staging is interesting and somewhat dependent on recording. On most modern recordings only a nominal turn of control to say about 1 to 2 o’clock will bring a sound that emulates a symphony hall in that the center image will expand and you will loose a tad of pin point imaging. IMHO a great way of killing the anal bred necessity of listening to your audio system to reassure your self that you are hearing all of the ’detail’ you think you paid for. A sickness shared by many otherwise normal audiophiles. :-)

I was not so impressed with its performance with my headphone system. It was OK but you had to tinker with the settings of each disc to get good response. Most of the high quality CD’s listened to sounded pretty good with out it.

It’s not very expensive. For the more adventuresome (or bored) audiophile I recommend it. BTW, for tubists, changing the single tube does make a difference. If you have a tape loop you have the perfect place for it.

FWIW

Far too soon to do or even think about any of that stuff - unit is not fully broken in nor is my understanding of its sound and use. I'm just having fun tinkering with it.