There aren't many 3ch options these days. XPA Gen 3 configured for 3 channels new, but since you're only adding the presence speakers I'd say your best bet would be either another used 3ch amp or even some old Marantz monoblocks - MA500 (150W), MA700 (200W) or MA6100s (150W) should be easy to find.
An integrated is an amp with a preamp that has no processing.