I have run into issues similar to this while using a windows VPN connection to our main office and found the following.
Be sure to limit upstream (and possibly downstream) traffic for any heavy use systems on your network. My dedicated torrent box has been set so that it doesn't eat my entire pipe and cause issues. Even with QOS enabled to prioritize VPN traffic it tends to drop if I saturate the link and increase the latency the connection has to deal with. The PPTP vpn connections are pretty finicky when it comes to latency they tend to drop VERY readily.
I also noticed in your question that you said you are streaming music over your VPN connection? Are you aware that be default Windows VPN connections are set to send all traffic through the remote default gateway? This is in place so that you can route to other networks via the VPN that may not be in the same subnet as your connection. You can easily get around this by disabing the "use default gateway on remote network" here:
Connection Properties -> Networking Tab -> TCP/IP properties -> Advanced Button -> General Tab
Once checked this will only send traffic destined for the remote subnet over your VPN connection allowing your streaming music to go out your local network connection without incident. I find this extremely helpful when you are trying to surf the web while working on a remote network, you get your local speed to everything except the remote LAN.
NOTE: if your pptp server device assigns IP addresses to your client system that is in a separate subnet than the network you are trying to get to you may have to work around it.
LAN Network address at remote site: 192.168.0.0/24
LAN network address at your house: 172.16.7.0/24
VPN subnet assigned to clients on the router when connecting: 192.168.254.0/24
This is the way windows server handles VPN connections when you use RRAS to host the VPN connections, and I have seen routers handle connections this way as well.
Workaround: you will either need to manually run a route command to add an entry to your routing table after connecting to the VPN, the command will look something like this:
route ADD network_to_reach MASK subnet_mask gateway_ip_of_vpn_connection
route add 192.168.0.0 MASK 255.255.255.0 192.168.254.1
This will tell your machine that it has to use the router at 192.168.254.1 to get to any system in the 192.168.0.0/24 network. Systems inside the network will be using the router hosting the connection as their default gateway so they will not need to be told how to get back to your system.
This can be automated and added to the VPN connection. This is how we manage and deploy clients at our office and it works EXTREMELY well. You can use the microsoft CMAK (Connection Manager Administration Kit) to build a VPN "connectoid" that contains automation instructions including routes to add, scripts to run during different phases of the connect and disconnect process, and some other goodies I've never touched.
Hopefully this will sort out your issues and get you VPN'ing while jamming to your tunes and help some others out there achieve a state of VPN ZEN.