Leben CS600 or ARC VSi60 with Harbeth Compact 7's

Out of your two choices i would go with the Leben. Because i have heard the combo. (have not heard the ARC)
But, I would think about manley or BAT also. I have made excellent music using both brands and harbeth.

Had CS 300 and have NCSE (SS) paired with C7ES3's. Either is excellent. My trials indicate room dimensions matters more than tweaking around for some magical piece of gear. Got a room you can dedicate to your gear measuring between 10 x 10 x 8 to 12 x 12 x 10? Close to ideal size space with C7ES3's.

Airegin,

Would you be able to articulate the sonic differences between the NCSE and the CS300? I am trying to decide myself between the LFD NCSE and the Leben CS600 for my Compact 7ES-3 speakers. Hopefully this would be instructive for all (as I am not intending to hijack the thread). Thanks

My stereo room is 12 x 17. The NCSE has a bit more grunt to it than the smaller Leben. Both the Leben and LFD are similar in being smooth and balanced sounding across the audio spectrum. That is what attracted me most to the Leben and the NCSE, smooth and balanced while capturing and resolving nuances within a recording. In the past three years I had three tube integrated amplifiers (Jolida 502, Rouge Cronus, and the Leben) with the Leben being my favorite of the three). The NCSE was my attempt to simplify things while retaining most of what I liked in the better integrated's I heard be they tube or SS. The LFD Zero Mk III (I owned one too) was a vivacious, entrancing amp, but lacked the refinement of the NCSE.

I just got an Ayon Spirit lll to use with Proac D2, I'd certainly add the Ayon to your list.