Atmasphere is right. My Vitus SIA-025 integrated uses a single Vitus-designed UI-core potted "floating" transformer with separate windings for the left & right channels. Isolating the transformer in a potted, "floating" magnetically sheilded enclosure certainly helps. Also being a true balanced design with well regulated power supplies helps improve s/n ratio. But yes, as a rule of thumb mono blocks usually sound better due to separate power supplies, reduced noise and lower intermodulation distortion as Atma said.
A friend whose ear I trust owns a Vitus SS-102 and Magico Q3's. He auditioned the Q3's with both the SM-102 monos and SS-102 stereo amp & preferred the SS-102 which sounds warmer and more tube-like, yet with similar resolution. Though the SS-102 runs separate transformers in a twin mono, true balanced design. Suffice to say, there are exceptions as mentioned.
A friend whose ear I trust owns a Vitus SS-102 and Magico Q3's. He auditioned the Q3's with both the SM-102 monos and SS-102 stereo amp & preferred the SS-102 which sounds warmer and more tube-like, yet with similar resolution. Though the SS-102 runs separate transformers in a twin mono, true balanced design. Suffice to say, there are exceptions as mentioned.