I own both the 1st Ice amp'd receiver Pioneer came out with, the ultra-flagship SC-09TX and the new SC-68 and both are excellent amps. I've been using their class D receivers for almost 5 years now and have no regrets with either one.
the new D3 design is not Icepower - it's a chip amp design from International Rectifier and has some theoretical advantages over the Ice amps: much simpler circuitry & no feedback loop needed to maintain low distortion across the freq band. class D amps have a switching frequency for the power supply that tells it how often to supply power pulses. in the Ice amp design, the switching freq was 50-60 kHz while the new D3 design is 10 times that, about 500 Khz so on paper the switching freq is even further away from audible range. in all class D amps the switching freq is removed by elaborate filtering and this is where the simpler design of D3 has an advantage over Icepower.
in any case, both have excellent sound quality, tight bass, can reproduce large swings in dynamic peaks and produce equal power to 5 channels at once without a lot of sagging, as opposed to some receivers with smaller power supplies that might deliver rated power in 2 channels but will really fall off when trying to drive 5 & 7 channels simultaneously.
and both amp designs are VERY capable of driving demanding low efficiency speakers (mine are 85 db efficient & need lots of power to sound their best, Magnepans) and lower than 8 ohm speakers. Pioneer finally gave a 4 ohm rating to their class D amps in last year's model.
go take a listen, and be aware that in comparing Pioneer to a Denon for example, the vast majority of any difference you may hear will not be due to the amps but to how the 2 companies room correction EQ works. Pioneer uses its own system, MCACC, and Denon licenses Audyssey.
and yes, there is an SC-68 & 67 thread which I started. come on over
btw- Home Theater Mag has reviewed every generation of SC models, including the first one, the SC-09, last year's D3 SC-57 and the new SC-68. they have nothing but praise for every one. you might want to check them out.