At 300 ohms you have 250mW for the Atom, 410mW for the Heresy, and 700mW for the 887. The Heresy is an excellent little amp, but yes the 887 does best it in measurements. Then of course there is the matter of features. The 887 wins in having XLR input and output, as well as a 3.5mm output.What does that mean. Reviewers keep saying that sound is richer when coming from a high power amp. is 887 considered high power or is it in the league of something like atom/heresy/magni with added bonus of lower distortion albeit already inaudible floor, better snr. I distinctly remember older hardware distorting going nowhere near 100%, but these things perform at 100% as well as normal listening volumes. But whats the point of distortion free even at 100%. Must be perks of modern electronics.
There is also the 3 gain levels on the 887.
Do the differences make up for the price difference? Depends on your needs and priorities