.+host user *!*@host (you can add as many hosts as you want for the user with any handle you want) so if it has the autovoice handle, the bot will voice him for all the hosts u added.
All you have to do to make your 'if' work is replace those ()'s with []'s to have the 'isvoice' executed.
In tcl brackets are used to perform "command substitution". This means what ever's between a opening/close bracket is executed (first word being interpreted as the command and any following words as arguments (read more about this here: http://tcl.tk/man/tcl8.4/TclCmd/Tcl.htm)) and the entire thing is then replaced by what's returned by the command.
Well u can do this: .+host user *!*@host
.+host user2 *!*@host
.+host user3 *!*@host
.......
where *!*@host is the same host.
and then .chattr user <flags> <channel>
so u can set the user autovoice on the channel u want it to only.
and then add your code.