You aren't using the second 5687. I suspect you're going to try 12B4 sooner or later aren't you? Good move IMO, but I would not throw a 5687 out ov bed either. The regulated linestage you heard in MD now has an RK34 amplifier valve. Two anode caps, mu of 13, and an 816-ish bottle. It looks quite cool.
regards,
Douglas