x4.1 have 7.1 surround sound and x4 have 5.1 surround sound.....
The one was a bit surprising.
With the X4's which use infrared I never once had an audio dropout or severe interference. The transmitter spreads a strong and wide infrared signal and the headset has quad 360 degree receptors on each side of the headphones. As a result I could face any directions absolutely anywhere in the room and never once had a hiccup. Even if I physically covered the receptors the signal would still bounce of walls and be picked up by the backside of them. Technically they say it requires line of sight but the signal bounces around the room enough that people walking in front of you, etc never interfered with it. The only way I could get the signal to cut off was to physically leave the room and go around the corner.
With the X41's which use rf I actually found them to have less range and a weaker signal. From my normal seating position(about 10 feet in front of the tv) they are pretty much flawless and about as reliable as the X4's. However once I move to the edge of the room(about 18 feet to the side) I start getting some mild crackling/popping. If I move off to the extreme side(where the entertainment unit blocks line of sight to the transmitter) it gets worse. The X4's had absolutely no problems in these are any other area of the room.
Once I leave the room and go around the corner to the spot where the X4's would cut off, I start getting severe and loud crackling and popping to the point where you have to shut the headset off.
Also the very odd time I would get some mild/soft crackling from my normal position...I assume that it's a bit of rf interference here and there.
One of the benefits I had hoped from the X41's was to be able to move around the house and still have audio(for listening to music, etc) but that's simply not possible with these. Their signal is pretty weak and they have nowhere near the transmission strength of a cordless phone or even the 360 controller. They are essentially a same-room only device like the X4's.