IMO you are mostly testing preamplifier combability - the 808mk5 can sound excellent but is not an universal preamplifier. And extremely powerful amplifier can sound underpowered with a non adequate preamplifier. As you say, high-end matching is more than numbers ...
Did you try a Burmeister amplifier with your 808mk5? When I listened to the 159 I was very impressed - extremely musical and powerful.
Just MO, but we should demo pre and amplifier sets, not single units. Surely YMMV.
Agreed. I have witnessed a friend auditioning a number of preamp/amp combos, where the preamp was a different brand than the amp, and the results were sometimes head-scratching.