Please correct me if I am missing something, but in the original post, it was stated that the primary issue was that when the volume was set, it was affected (lowered) by using the phone. I assumed from this post that the overall volume of the system outside was adequate (as you adjusted on the 190) but that when you "use the phone" the system volume drops.
If this is still an issue to consider, can you explain in more detail this part of the issue? When you say "use the phone" are you describing a phone call, adjusting music and also volume? I would be curious if you started to play music from your phone to your system and then adjusted the volume on the 190 directly, and then use your phone to advance from track to track, would the volume still decrease (making sure that you never press any volume button, slider, or control on your phone. It seems to me this could give some guidance on whether this would really be a function of a BT dongle.