Hi, I too have ART-7, it is indeed very good, however, the very low output can be problematic, I'm a keen DIY'er and have built my own MC preamp based around the Linear Tech LT1028/LT1115 op amps which most high end HIFI companies use or should use.
If you're interested: when designing an MC pre amp for extreme low output, power supply noise rejection becomes more apparent, thats the issue I had and have since rectified this problem with lots of head scratching and testing with different ways.
On the MC pre amp I have 100ohm loading for the ART-7 with 60db of gain, it is low but all this means is you have to turn the volume up on the amplifier. I'm happy to live with that.
Let me know if you need more info...