I've done it with a B-15 head and an H&K Red Box Classic. Best DI sound I ever had. Sounded very much like a REDDI. An all-tube design is the best candidate for it. Really doesn't make a difference in solid state or hybrid amps unless they have an output transformer. Maybe an Aggie DB 750 or a Warwick Hellborg would be a good candidate for it. Otherwise, post-preamp is about as good as it gets.