When I asked the very helpful Engineering Director at Airlink Transformers in the UK about this, he said to add up all the transformer sizes (in VA) of all the items that would be powered via the BPS (Balanced Power Supply) then double this value to determine the minimum recommended size of the BPS. Taking this guidance, we arrived at a 3kVA size but for an extra £50 or so, we could have a 5kVA one, so we bought the Airlink 5kVA BPS. It has been brilliant.
Threads about Airlink BPS appear on the Naim forum every 6-12 months, so if you search for Airlink posts and my name, you will find a lot more background.
Hope this helps, BF
