Hardly any difference with PCM 705.6. Closed has CPU cores at 0-5% with minimal GPU (1-2 %). Closed Mega has CPU cores at 1-5% with similarly minimal GPU. Pretty sure I couldn’t pick between them blind.
I have the max PCM and DSD rates set to 705.6 and 44.1x512 because something goes wrong in my system with 768/48x512. I think it’s in my DAC.
With poly-sinc filters source material in the 48k family gets output at 44.1x512, but the closed form group of filters are not poly-sinc so the output drops to the max supported rate for 48k.
I will preface this by saying I don’t really understand filters and can only go by what I hear, which could be way off base!
Closed-form mega is a very smooth sound. The body and presence of vocals sound natural.
It has been noted by many listeners that poly-sinc-xtr seems to attenuate high frequency (when I understand the measurements show the opposite? a greater HF extension.) I find in practice it actually enhances HF detail—the utter absence of edge reveals more what I have heard some call “inner detail.”
Closed-form shines, imho, in the midrange. Well-mastered recordings of small combos with vocals for example, are stellar. But I think this exceptional midrange quality can cause a perception of relative edginess in the top end. The recordings where it falls short are often very busy productions, especially modern masterings. The trademark impressively wide soundstage is still there, but it seems to a contiguous mass of sound rather than an image with distinct elements. With poly-sinc-xtr-lp there is more separation and thus clarity and detail.