Hi Kushanava, I don't have expensive sources. I have a Sony 5400ES CD player, an old Technics turntable, an old Kenwood tuner and an HRT iStreamer DAC. I played all those sources through the ATC scm-11s with the M3i. I didn't find any of them harsh, but they can be fatiguing if the recordings you like are bright and busy. If you mostly listen to good recordings, these can sound fantastic.
Overall, I would describe these speakers as clear, punchy and neutral. Tonally they are natural, but not warm or rich. I did not find them exaggerated in any way, yet they were not boring because they have good dynamics. Soundstage was very good but not exceptional. They do height and width better than depth with that amp. Music is clear and well organized. They play confidently down to around 60hz, bass is tight and controlled, but not deep. I used them with subwoofers. I listened to these about 8 feet away. Optimally, I would set these back a bit farther, say 10 to 12 feet, and give them more volume, I just didn't have the space to do that. If you can turn them up, they really come alive. They are dynamic and confident at higher volumes. It is very enjoyable, but if you sit close you find yourself turning them up to get to this point and then they can be fatiguing because it is simply too loud. They are sealed boxes and they can go close to walls without much issue. They are very well built.
If you are concerned about brightness or you like things a little warm, I would try to audition these first.
Ryder's Quad suggestion could be a good one. Spendor may be also if you are concerned about brightness. I haven't heard Spendors with MF gear though. I don't know how that will sound together.
