91-01 300B monoblock amplifier has earthshaking sonic performance (see PFO review).
1. 91-03 300B dual-mono stereo amplifier has sonic purity, while 91-01 300B mono-block amplifier has the vintage golden warmth..
2. 91-03 has more advanced power transformer and output transformers and superior power supply and fancier big aluminum chassis + a built-in volume control preamp. If someone does not have a high end tube pre-amplifier ($3000 or better), then 91-03 is a natural choice for one box solution.
3. 91-05 is the current flagship 300B amplifier, can be used with or without a tube pre-amplifier. It is a bargain at $10,000 to compete with other companies in $10,000+ market and still enjoys a comfortable margin for sonic performance. Thanks for the very best Output transformers and the best execution for magical sound.
If you can go for 91-05, then it is an amplifier for many years of enjoyment. It is the best we can do for one box solution. 91-03 is the second best at reasonable cost. 91-01 is for someone who has a tube pre-amp already and would not mind for plain black steel chassis. Every Sophia Electric amplifier has magic sound. Sophia Electric has a secret recipe for magic sound.