Yes, thanks for quick reply.
As I wrote, I've had a lot of respect for GPA and previously had personal contact with Bill (and Todd too, long time ago, by all means), and I've bought for several thousand dollars from them over the years (despite shipping costs and VAT to Sweden...).I just wanted to hear a secondary opinion, so to speak.

So I guess I push the button then and buy a pair of HF-diaphragms to my 604 for total $378 (which is half the price before they opened a Europe reseller!).