The products on Keith's website represent his new line. They evolved over 20+ years. I had the M1s and then had him upgraded them to the M1As. I am not sure if there is a M1A to M2 upgrade, but am happy with my M1As and my CJ tubes. You would need to call Keith and ask of there is a M1A to M2 pathway. But remember, in some cases the difference between the old and new models may be too great making an upgrade impossible or very, very expensive. I have had my Herron amps since 2005 and I, like many people, hang on to their Herrons. All Herron products will resell, but the used market for all equipment was damaged ~10 years years ago so you cannot always expect to sell used products at a price that you may want. The CJ ET5 is a good example of how 2-3 people dumping their preamps deflated the market. A used ET 5 should be selling at $4500 not $3400 or lower. It is still a fabulous preamp. And, then again, many older products simply have lower no resale value. So, do not let the false prices set by the used market impact your decision. Pick the product that makes you, your ears, and your wallet happy.