I took a chans that im not sad for it was a very good choice to buy XTZ Sub Amp SA-1. Mario at Fyndbörsen send me a email and asked if i would use it for. If it was one of XTZs made subwoofers or if i have other thoughts.. I asked why he asked that question and simply explained that he could install the right firmware if it was one specific XTZ sub i build my own with a Dayton Audio 15 model: RSS390HF-4 ok he said that i leave it on the neutral firmware then please dont be afraid to write back if something is on your mind about the sound sure no problem i said. I build a closed enclosure with 22 mm MDF the volume i choosed was 94 Liter +VD 15 Liter stiffened it up with MDF it takes almost noting in vd. Filled upp with maybe about 65% of pollyfill made a thicker wall on the back side so the amp not would have anything who could jam the circuits made a air gap on the under side and of the over side so the little heat that the Amp leaves has some way to ventilate. And now to the listening it didnt take mutch to get the settings right i owned an Earthquake Supernova MKIV that i have refurbished and thougt that sound good... The XTZ Sub Amp SA-1 with Dayton is mutch better sound it goes deep under 20 Hz as nothing now i could heare the sound and feel it before i felt it but it was nothing in compare with this the bass sounds better overall and the SPL are louder and the sound is clean the walls are shaking plenty so i had to make plenty of stuff so the vibrations dont disturb the movie or deep bass notes exelent combo can i say i have heard mutch in my days but that this would be so great i did not know u should try it dont be afraid if it sounds to good.