Unsound,
A dealer was telling you that the 2Ce Sigs won't reach their true potential unless you drive them with something that's 200 watts...
That just seems a little silly.
Driving them with a 175-watt integrated does give them some more "headroom" than a 50-watt integrated (I guess that's the way to put it), but I just don't want you thinking that it's going to be worlds of difference.
The gear you already have should be plenty good!