Mercury Magnetics transformers are simply higher quality transformers in many cases and they are often tweaked in their designs to be better suited for the amps they're going into. If you put a properly designed output transformer in a silverface Princeton that sounds flubby when it's on 10, a MM transformer may certainly help, because most guitar amp transformers are weak. Now the stock transformers sound great in tons of amps, but everyone has a flavor. Quality is often associated with louder or deeper sounding. It's a proven fact that cars with heavier doors are perceived as more valuable, so imports are designed to be louder than necessary when you close the door. Also, just wondering, does anyone have any experience with the Kempler Profiler amps? They sound like incredibly innovative technology but it takes some great trust or experience to throw that kind of money on a modeling amp. Is it really that good at what it does?