I am sorry but this is all BS, Mr. Thorioki. Not one word of this can be true.
No preamp can destroy a speaker, unless it is transistor junk and sending infrasonic (sub hertz) into a cheap transistor amp ( which would have blown the fuse). No tube preamp can send DC into an amp. Capacitors 'failed' you say? BS...that would have blown the fuse in a microsecond..
A tube amp, never mind about a preamp, CAN NOT send DC into a speaker, the exception might be SE by a cheap company with no protection, but never a preamp and never a transformer based amp such as the Prima Luna.. If your preamp sent DC into the amp, you would have zero sound EVEN if it was directly coupled (meaning no capacitor or transformer coupling)...why, because you have sent the preamp tube into cutoff, and likely blown the fuse.
Kevin Deal must have laughed you right out of the store.