I have beosound ouverture, is necessary beolink wireless to link beolab 3500 or beolab 2000?

A beolink wireless is only required if you cannot connect the speakers to the beosound directly with a masterlink cable.  In this case, you would need at least 2 beolink wirelesses (one as a transmitter, the other as a receiver).  Also, I believe more recent versions of the BL3500 also support a powerlink connection (I have one with a powerlink connection socket, but have never used it so I'm not sure if there are limitations regarding its use).

Be wary of the beolink wireless.  Many members have had issues with finding proper the placement to get good results.  It can suffer from interference with cordless phones, microwave ovens and wireless internet.  Also, heavy walls can limit the range significantly.  I have a pair and they work exactly as they are supposed to, but I seem to be the exception rather than the rule.

Stan

Stan I'm really glad yours have worked, for us we have found the Wireless Kits about as useful as a chocolate tea pot.

Yes, I seem to be the lucky one.  It took me 3 tries to find the right placement - luckily I already have a lot of ML running through the house so I had some options that were not difficult to test. 

I transmit from a shelf behind my BV8 in room on my first floor to a room directly above on the 2nd (maybe 10ft total distance).  It's about 30ft away from my wireless base station and 20ft from microwave (and I believe my refridgerator does some shielding of the microwave at it stands in the path between microwave and wireless).  Nobody can really walk between the transmitter and receiver (this was a problem in my first placement).  There is sometimes some interference with my BeoCom1 (clicking in the background while talking), but this doesn't impact the wireless.  My neighbors are far enough away that their wireless networks do not interfere (I can see 2 or 3 networks from my house, all with no more than 1 bar).  The timer function is not 100% reliable - about once or twice a year, it will turn on (the lights on the speakers go green), but no audio is played - hence, I have a BS3 for backup (the BS3 predates the wireless).

I think the cheap construction of homes (wood and drywall) in the US tends to help, although even my dealer said they generally do not recommend the wireless as  they usually "come back".

Stan