We are happy to hear that you upgraded to the Slingbox 350. Thank you for posting to the forums. I am sorry you have so many concerns. In regards to your first concern. the audio video sync issue, I would suggest that you check out the following article and see if that helps.
In regards to the second issue, check out this article, it may help with the Roku.
Then the last issue you are having in regards to the controlling, which I believe you are meaning the virtual remote. There is a delay from the time you push the buttons and the time in which the selected function occurs on the video displayed on your Slingbox. If you do not already have the external IR emitter plugged in, then you may want to plug that in and see if that helps the delay time.
Hope this helps. Happy New Year.
The Sling Moderation Team