Yes I am using 4ohm speakers on both my rear parcel shelf speakers (MB Quarts) and my SWS-8's. Actually it didnt freak out the head unit, but since the MB Quart speakers were rated at 4ohms and higher wattage than the stockers, I had to add a small 2 channel amp to drive the rear speakers, so I could adjust the gain to balance out the loss due to the higher resistance. All in all my system sounds fantastic, at least from stock.

I didnt reuse the OEM rings, I just used 3 of the 4 tabs and made one new hole. Seems to work fine for me under the speaker grills.

Be careful when you set up your sub amp to push your SWS-8's, as if you push them too hard they will blow on you. Its a fine balance, cause it they sound so much better than stock, but there is limited space under the floor and the door cavity, so although you will get outstanding performance you wont get license plate rattling bass from the two 8's, but it IS a vast improvement!!!

 

I've checked their FAQ myself and according to an update in 2009, they will ship to Europe but do not guarantee it will fit the basic version, i.e. you are on your own! So I'd still appreciate to hear from anyone who might actually have taken the plunge?