Beatsonic do adapters to fit aftermarket head units retaining factory audio and cameras but they are pricey £200+ .
http://www.world-beatsonic.com/category/search/toyota-search/alphard/
I saw your post noting no-one had replied.
I can't help with Thule but thought my experience might helps.
I bought a "pukka" Whisperbar Kit from www.roofbox.co.uk for reasonable money and excellent service.
Since bought Yakima Kayak carrier from them too.
If I remember correctly they have thro-bar and flush versions which use the Alphard anchor points.
Checkout www.whisperbar.com.au
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