Now seems like a good time to switch over to an HDMI rather than VGA cable and the connector is exceedingly tight which made that a bit of a battle and took a couple of forced reboots to wake up (turns out I had forgotten to change the BIOS settings so was looking for a PCIe card).
Now the machine is running I can start to get an idea of sound levels and actual vibration through the case.
I can safely say that the case has zero sound dampening capability.
The Samsung BD drive sounds like an aircraft taking off until it spins up (we've only got plasterboard walls and it sounds clear through the walls, luckily it's only while spinning up). The Hitachi drive is a nasty rattly thing. However, the single noisiest thing is now the power supply - it's not the loudest in volume but as its fan is spinning constantly it is a continual noise. I've cleaned all the dust out which helps keep it cool and I've also removed the rear wire grill - there's little chance of small fingers getting pushed in there where the unit will be located finally and the removal of the grill notably smooths the air path reducing volume. Still noisy and for a fairly quiet PSU that was a surprise to discover. Am I going to replace it with a silent model? No, not a chance, the silent standard PSUs are all much higher wattage than I want or need so are likely to be less power efficient and the ones with external power bricks give me limited options for drives (now 4 in the case) and it's just more money.
Testing further with the lid on though does demonstrate quickly that outside of the aircraft drive spinning up the others noises are at an acceptable level even close up - I don't really mind the hard drive ratting when it's doing something and at a couple of feet none of the noises are problematic and by the time some media is playing it's not noticeable at all & I'm really picky about this sort of thing so I am pleased that isn't going to drive me to distraction.