you are a bit confused, yes
there really isn't much difference between 2113 and 2313 in this regard, both are 7ch amps with zone 2 capability.
1. if you want to power Zone 2 with internal amps, then you have to run a 5ch setup, because there are 7 amps and you are using 2 for the other zone (leaving 5).
2. if you add an external 2ch amp for Zone 2, then you can maintain a 7ch setup in the main zone while powering the zone 2 speakers (because you now have 9 amps total, 7 built in plus 2 external).
3. regardless of both of the above, the amp is only 7ch so if you want to run wides or heights you cannot run surr.backs. This has nothing to do with zone 2.
the only major difference as far as you are concerned is that the 2313 has DSX (allowing you to run wide speakers, although again at the expense of surr.backs). Both have PLIIz so you can still run height speakers with the 2113, but the 2313 gives you the addition of DSX for heights or wides.
second, the 2113's zone 2 pre-outs (which you will have to use if you want to maintain 7ch setup in main zone) are fixed level, meaning you must control volume via an external volume control (either the external amp or an in-line volume control, e.g. a wall-plate you install in the zone 2 area). The 2313 (assuming it's the same as the 2312 last year) allows you to set the zone 2 pre-outs as "fixed" or "variable".