The A860 that Audioholics tested/reviewed (and, presumably the A870 that came after it) was recognized as having a comparatively anemic amp section!
Accordingly, I would keep the 1502 for your R&L mains where it will do the most good!
One caveat is that the pre-amp outs are a little on the weak side if your amp does not have enough gain. I am not sure how the 1502 fares on this count, but hopefully someone else can address this.
See first paragraph here:
The Yamaha AVENTAGE RX-A860 7.2CH Atmos/DTS:X AV receiver is packed with excellent networking features but it does fall short on power delivery making our recommendation conditional based on usage.
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