Cpcorreia,
I agree it is a risk and it may be worth it, so perhaps you just have to try. However, I would be prepared to forgo the Soulution and try at least 1-2 other amps for direct comparison.
As I said, I've spoken to a number of Isis users who have moved-on because I believe they did not strike that synergy with equipment or room. What the Isis really do well is to convey the weight, scale, and perspective of large pieces, but it requires power. If you can play a large orchestral or choral piece, close your eyes, and have a fairly accurate representation of the orchestra and the hall, you are done. If you are not getting that, then the speakers are not doing what they can do.
Paradoxically, I found that Pass to sound more effortless and majestic than the Karan's. I attribute this to the pure class A power among other things. The Karan's put out over 2kW into 4 ohms, so they are a real force for power. There are not many amps on the market which require two power cords per chassis. I still remember ordering new fuses for those amps, and someone from the store called me to make sure I ordered the right ones because they were rated for an incredible amount of current.
If you must keep the Soulution and have no flexibility with the amp, I might recommend you look at other speakers. If you've decided on the speakers, can be flexible, and willing to experiment, you can be rewarded.
