You could use an external amp for any of the pre-outs for which you seem to have 7. On my Yamaha processor there are an 4 additional pre-outs for front and rear presence speakers. This does not appear to be the case with the 2050. Sometimes it is a hybrid option where Zones can be re-purposed and here you do have the speaker terminals but not the pre-outs. However I think from
@snakeeyes comment your maximum would be 5.2.4 if you want all the heights.
