Something better than Marantz PM7000N at around $1000?

I’d say that right now it’s unique at the price point for the feature set (amp + wireless + streamer + dac + bluetooth), so if you need all those, then the answer is no, there is nothing better for the price.

What do you mean by asking if the B1 could be better? You’d only use that to add bluetooth to an amp that doesn’t have it. Most every mainstream (NAD, Cambridge, etc) integrated has BT nowadays.

Considering just the sound quality, would B1 + int amp (near $1000) be at least as good as other int amps with a built in BT?

The maximum sound quality of Bluetooth is pretty much the lowest of all digital inputs. I think most BT receiving circuits and chips are generically implemented at the line-level, so the variable performance of BT (e.g. B1+amp x vs BT-capable amp y) is likely to be trivial when saying which amp you prefer overall. That’ll come down to power supply, the transformer, component quality, gain stages design, compatibility with your speakers. Home demo + your ears are the best way to decide which amp is best for you.