The big 6 is a fundamentally different technology to the Atlantic and 7 series.
The Big 6 was a NOS multibit chip using small dual triode output tubes.
The 7 series and the Atlantic both use discrete R2R ladders for PCM and discrete "chipless" architecture for DSD. There are NO Dac chips in these units. On top of that, the output tubes are now Directly Heated Triodes (power amp tubes) for the output in the 7 series and 4P1L pentodes run in triode mode for the Atlantic line.
They are VERY different to the Big6 and to the old Level4.
Incidentally, I have never been a big fan of the Big 6.
