What are the four conditions?
I enjoy Hi-Fi with almost no money investment but homemade cheap creative solutions answering to the 4 conditions :
1) Vibrations-resonance controls of the audio system embedding...
2) Conventional acoustical room treatments...
3) Cleaning of electrical grid of the house and room...
4) Tweaking with supplementary non conventional method for acoustic transformation of the room, for example modified Schumann Generator, Helmholtz resonators, and other type of resonators... And some others...
My best to you volumizer