The Odyssey Extreme Mono Amps I use are said to push 300-350 watts into 8 ohms, much more into 4 ohms (the I's are 4 ohm speakers). More important is they push in excess of 150 amps of current through the speakers, which is where the control conmes in. High quality power brings out the best in these speakers.
I highly recommend the upgrade for the 12" sub. Not only does the added SBA circuit bring the bass response lower, but the port tuning helps tremendously. I get firm, musical bass response below 25 hz. I have not upgraded the crossovers. When I talked to John Strohbeen about it, he told me the upgrade would not be audibly noticable. Basically, if the original crossover worked fine, just stick with it. He gave the same advise about the 1" tweeters. If its not broke don't fix it.
I have not heard any Thiel speakers. The only reason I mentioned them, is they seem to have a footprint and size similar to the Ohm I. I have read more about them recently, I think I'll be looking in another direction. Not that I am really looking. As I mentioned before, I have tried the Walsh series speakers. I had a pair of Walsh 4XO cabinets with the Walsh 200 Mk2 drivers in them. These were the traditional pyramid style cabinet, which I like better. They did not have the top end or deep bass of the Model I, but I felt they had better imaging. I would have kept them, but had no place to put them. The Walsh 5 Mk2 that I have in my HT room are the newer tall rectangular cabinets. As I said, I really do not know how good they sound yet due to acoustical problem of the room they are in. Whenever I get a dedicated audio room built, I suspect I will prefer the Walsh 5 over the Model I.
What other speakers have you heard that you know are better than your Model I's? Regardless of price?