Perhaps using a 'musical instrument' as an example is a bit misleading, as you say, the instrument is designed to work with more limited frequencies to produce those sounds. I've always found on modest sized cabinets, your latter example, using a more rigid cabinet using steel with carbon fibre where possible to keep the enclosure light but very stiff works well - it's surprising how little damping is required if the cabinet is tuned and braced correctly. My point was really to say that mass damping can lead to lifeless, dull sound.
I think I'll be ordering some of the Alcaps from Falcon, I can't see the originals fairing too well - the 72uf measure well out of spec.
Still haven't heard anything from Wilmslow about the 22uf Mundorf E-caps supplied as RAW not PLAIN.... not good customer service.