A little late to your party and you've made a decision I'm sure, but I am so delighted with my GNSC Opus 21, I thought I'd chime in....
I have not heard the modified 55 or the stock 55 for that matter, but I have now used/owned a stock Opus, as well as the GNSC Opus. I must say, the modified Opus is head and shoulders superior to the stock Opus. If you can swing the modified Opus do yourself, as well as anyone else in the home, a favor and get it! If you can't afford it, I will speculate the modified CD55 will better the stock Opus. The GNSC mods are that good. Hope you've contacted Steve, he's a good guy to deal with....
I have not heard the modified 55 or the stock 55 for that matter, but I have now used/owned a stock Opus, as well as the GNSC Opus. I must say, the modified Opus is head and shoulders superior to the stock Opus. If you can swing the modified Opus do yourself, as well as anyone else in the home, a favor and get it! If you can't afford it, I will speculate the modified CD55 will better the stock Opus. The GNSC mods are that good. Hope you've contacted Steve, he's a good guy to deal with....