A dedicated TFTP/MOH server will be basically a Subscriber in a CM Cluster having your Publisher and Subcribers. In this case the MOH/TFTP server will only have TFTP, MOH Audio translator, IP Voice media streaming app, and Database layer monitor service running on that server. No other service should be started/activated on the dedicated MOH/TFTP server if need to be. As soon as you activate/start the CM service it will become a registration point and do call processing for devices.
Usually the MOH server will register to whichever CM is primary registration point all the time otherwise failover to next CM server in the cluster. So to dedicate an MOH server all you do is on the 2 x 7835 you may or may not want to Set the "Run Flag" from Yes to No to disable CM to be a MOH server and only have Run flag set to the dedicated MOH server.
Then again you may want redundancy with MOH servers, thats up to you.
Make sure MRG and MRGLs are configured correctly for phones to use necessary resources MOH server.
May want to go through the SRND on MOH.
http://www.cisco.com/en/US/products/sw/voicesw/ps556/products_implementation_design_guide_chapter09186a0080447511.html
-Yavuz
