Have had the same experience. Contacted Sennheiser Netherlands - they support-guy said he tested the BTD500 with the momentum 2.0 and it should work fine... The dongle must be defective, he said, so I had it replaced. Guess what? Same problem..
So the conclusion above seems to be correct... thanks Sennheiser NL...
Does anyone have experience with other BT-dongles to stream apt-x from a windows-PC? Which one supports that?
(Meanwhile very happy with my Momentum 2.0 Ivory; even used it while mowing the lawn yesterday
The problem may be that the Senny Dongle is old like the Chinese Wall and uses Bluetooth 2.1
Alternatives?
As a dongle, I have tried and actually use the Azio BTD-V401. It is not independent as the Senny, it needs drivers and software: the CSR Harmony. It comes with it but you better download the latest version from Azio website. You must at first install the program (and at first disable the bluetooth Service of Windows) and only after that plugging the dongle.
It should but is not able to provide enough bandwidth to a mouse and a headphone at same time, so if you use it with a BT mouse you have stuttered sound.
There are also these two from japan:
http://www.amazon.co.jp/gp/product/B007PVKOO4/ref=ox_sc_act_title_2?ie=UTF8&psc=1&smid=AN1VRQENFRJN5
http://www.amazon.co.jp/%E3%82%B5%E3%83%B3%E3%83%AF%E3%82%B5%E3%83%97%E3%83%A9%E3%82%A4-Bluetooth-USB%E3%82%A2%E3%83%80%E3%83%97%E3%82%BF-class1-MM-BTUD43/dp/B00HX64XUM/ref=pd_sim_computers_1?ie=UTF8&refRID=1BZSCPHH9FTQRSVJF7YT
They are not only aptx but also Class 1. Which should only make a difference when connected to a class 1 headphone (only the Plantronics Backbeat Pro are Class 1 unfortunately) but I think it will make a little difference also with any other headphone, giving a slightly better range.
You can find them also in www.yodobashi.com and in Rakuten Global
Then there is the Creative BT-D1 and BW-D1. I still did not understand the difference, and the answer of their support was hermetic.
Most people just buy the BT-D1. It is like the Senny, independent, no software needed.
Then there is another alternative: the Avantree Priva. It is a 3.5 adapter, so theoretically there should/may be a degradation of sound due to more passages (from digital to analog, from analog to digital, and again from digital to analog). But I did not notice any difference with Azio and Senny.
They made a new version, I have just skyped with the Product Manager (I am a tester), I am not sure if is already available. The difference is a better sleep time (for tv shows where there is lot of silence, the thing was going in sleep mode), an automatic power function when connected via USB to the TV, and the Aptx also works in Dual Link mode (you can connect TWO headphones at same time and both listen to the same music or tv show, both in Aptx. The old one was using the SBC codec in Dual Link mode).
They are also making a new bigger adapter, a receiver/transmitter, with better range and also optical connections. But not yet available.