I was exactly in your situation. The post which gave me the final solution was this one from roms :http://mitelforums.com/forum/index.php?topic=2800.msg22057#msg22057
Note in the end :
in some situation (not for me), you may have to rename :
L2Boot_5340.bin to L2Boot53xxTtn8M.bin
MinetIp5340.bin to MainIp5340.bin
You can try this first.
But when I have updated with the firmware given in this post, I had this in the TFTP log :
Read request for file <L2Boot53xxTtn8M.bin>. Mode octet [24/06 20:36:06.864]
File <L2Boot53xxTtn8M.bin> : error 2 in system call CreateFile : File is not found. [24/06 20:36:06.864]
Connection received from 192.168.1.149 on port 49158 [24/06 20:36:06.868]
Read request for file <L2Boot_5340.bin>. Mode octet [24/06 20:36:06.868]
OACK: <blksize=4096,> [24/06 20:36:06.869]
Using local port 55043 [24/06 20:36:06.869]
<L2Boot_5340.bin>: sent 25 blks, 99344 bytes in 0 s. 0 blk resent [24/06 20:36:06.939]
As you can see, if it does not find the file, it tries the other name.
But the system still needs the MN_Generic.cfg file. About this question, see above, the post of randalk :http://mitelforums.com/forum/index.php?topic=2800.msg18618#msg18618
Get the files he attached, adapt them to your needs. Probably the only edit required is the type of the phone which must match.
Change the name of the file with the MAC address to what your phone asks (MN_08000F683D49.cfg)
When I have done all that, I got at last the login of the Web Configuration Tool.
Login : admin
pass : 5330
And the configuration tool appeared ! I was able to setup the phone, and it works.
Hope you will be able to do the same.