Off-hand, there are few integrated amps that I know of with an ability to disconnect the power amp section and drive it externally. I have one - the Bryston B100ST, which is discontinued, but it is in your price range as pre-owned.
The somewhat newer B135-SST2 also has this feature below $2K. The latest Cubed models are above the price point.
Integrated amplifier from Bryston. I would rate it a 9/10. It's been in the box the past 4 years. Recently back from Bryston where it was cleaned and got a clean bill of health.
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