Thanks sam, coming to your questions...
1. I use a TP-Link router rooted with DD-WRT firmware and I use the local broadband cable modem with the login/password mechanism. The reason I need to ask for reset of the MAC with the provider is that if I make any changes on the security or any other settings (I am not specific as I will check it later on my router and report back) the internet access is disabled and then I need to call up them to reset and it again works fine.
2. I think I need to read more on DNS service as I can utilize the same as per your recommendations above to make the changes on my router to stream Spotify on my devices.
3. What I wanted to achieve is that rather than making any modifications on my main wifi router can I connect a wifi repeater (or something similar router) and then make the necessary DNS settings on the repeater and connect only those devices/services like Spotify/Netflix which require the location specific access. This way I can utilize my main router for regular usage and the different router for specific applications. I hope I made it clear now.
4. Coming to the device I have a "
Rocki" play device for wifi audio streaming from mobile/tab etc., and not Roku which is also similar kind of streaming device but for video/audio. The Rocki is only for audio streaming and I think they have a Rocki+ with a HDMI interface for video streaming as well.
Edit: I just read it online that if I use the DNS service settings like say US then all my internet traffic will be routed through this DNS rather than my local ISP providers. Correct me if I am wrong. If this is the case then I wanted to avoid as I cannot utilize the full bandwidth of my entitled plan of 25mbps (at least half of that at regular intervals).