Sharon,
there are as many opinions as there are individuals.
I would not necessarily rush out to buy Imax 1 since you already have number 2 and find it a challenge. You may prefer to get Circuit Max for now, for example, if you are looking to spend money on a tough workout and the different style of Circuit Max will challenge you in different ways.
Personally I find Imax 1 tougher than Imax 2 but there are several factors at play here and whether you or others find it tougher or easier than Imax 2 will depend on how your body reacts to those factors that differentiate the 2 videos.
Imax 1 has most of the interval blasts done off the step, and the same movement is repeated for the whole minute (continual star jumps or power scissors, for example) so there is no variation and it can be a bit grim sometimes thinking that you are stuck in a move you find exhausting for a minute with no respite. A minute will never have seemed so long...... Imax 1 is therefore a greater psychological battle I find.
The blasts in Imax 2 include variation so while the intensity is maintained, you get to do several different moves within that minute, and for some people this matters (me!!!!) because you are then able to mentally push further for longer. The blasts in Imax 2 are primarily on the step and so some feel Imax 2 has a dancier feel. This explains why A-Jock overwhelmingly prefers Imax 1 which is athletic through and through. If you are someone who prefers Step Works and Rythmic Step to Hi/Lo and circuit style workouts, then Imax 2 will be the interval workout for you.
Again, musical taste is such a personal thing, Imax 1 has mono-thematic music, there's not a lot of variation, it's more of a steady thumping beat keeping to the time of the minute's blast. Imax 2 has songs sung by real people and some are motivating in the extreme. I would say that if you are someone who tunes out the music as background interference and prefers steady state instrumentals, then Imax 1 will suit you. On the other hand if you feel your motivation waning and you need some rocking music to get the blood pumping, then Imax 2 is truly magical and does this for me every time.
There are times when I dread Imax 1. I never dread Imax 2, everything about it suits me better and it leaves me feeling like I've flown to the moon and back, it's such a rush.
And again, there are many opinions out there on warm ups. I hate the warm up of Imax 1. I hate to start getting jumping in the warm up leaving me tired already by the first interval.... I find the warm up too high impact so I always modify it to low impact at this section. This warm up seems nothing to rave about to me, my fave of all time is the warm up to Rythmic Step. But everyone's different!
Hope this helps
Clare