I have an Opus 21 stack, consisting of the Opus 21 CD player, power supply, s30 integrated and XS ("Extra Sources"). Mine, too, was modified by Great Northern Sound. I understand that the C-50 is based on the s30, which had lots of good low bass, provided that you don't mind living within the power limitations of a 30 watt amp. I listened with my Verity Parsifal Ovations, and they sounded fine at moderate volumes; I don't listen too loud under any circumstances. I use my s30 now with Spendor LS3/5a's in a very small room and find that highly satisfactory, all of the volume limitations above restated here for this outfit.
I understand that the C-50 has a lot the same sound as the s30 but has a bit better resolution and twice the power. Since Steve Huntley is representing Resolution Audio now and has a ton of experience with both the s30 and C-50, why don't you contact him at Great Northern Sound Company (651.351.5355) to get his input. He is not a dealer anymore and would refer you to a dealer near you if you want to purchase a C-50 but he is a straight shooter and his opinion is likely to help you.
I understand that the C-50 has a lot the same sound as the s30 but has a bit better resolution and twice the power. Since Steve Huntley is representing Resolution Audio now and has a ton of experience with both the s30 and C-50, why don't you contact him at Great Northern Sound Company (651.351.5355) to get his input. He is not a dealer anymore and would refer you to a dealer near you if you want to purchase a C-50 but he is a straight shooter and his opinion is likely to help you.