My SLP-05 is a treasure. It uses 6SN7s (I imagine the ARC uses 6922s or 6H30s),which to my ears is generally a "ballsier", richer, bigger sounding tube - particularly in this circuit, but without sacrificing air or detail. It sounds as if this may be the ticket for what the OP is seeking.
I've not heard the LS27 and am not denigrating it in any way - ARC is a venerable firm which produces many superb components.
I've not heard the LS27 and am not denigrating it in any way - ARC is a venerable firm which produces many superb components.