I've not heard the 30.5, but used the old Aleph 3 for a good few years and loved it. It was certainly one of the best amps I have owned. I currently own the ARC Ref 75 and I concur with everything Esharp says. An accurate, detailed and dynamic amp, but with a rich, full sound, that doesn't compromise that neutrality. I have compared it with it's more powerful ARC reference brethren and I actually prefer it.
I am not a fan of magazine reviewers, but a very experienced UK reviewer who has used ARC for years and bought the 75, commented that he felt that 50 to 100 watts was often the sweet spot in the ARC Power Amp range and he preferred the 75 to the more expensive 110 and 150 amps. I know there are better amps out there, some like Dartzeel and D'Agostino momentum amps, that I have heard myself. You are going to pay multiples more to improve on the 75 though, in my opinion.
I am not a fan of magazine reviewers, but a very experienced UK reviewer who has used ARC for years and bought the 75, commented that he felt that 50 to 100 watts was often the sweet spot in the ARC Power Amp range and he preferred the 75 to the more expensive 110 and 150 amps. I know there are better amps out there, some like Dartzeel and D'Agostino momentum amps, that I have heard myself. You are going to pay multiples more to improve on the 75 though, in my opinion.