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Brendan, I’ve seen some excellent images taken with a C9.25.
R+IR would be something like the Baader R610...has a wide bandpass so shouldn’t block out too much light.
To keep your expectations real, start out at f/10, and then try a 2x Barlow. Doesn’t need to be a fancy one given the size of the sensor in the 290. Ideally, f/15 is the sweet spot for it, but 1.5x Barlows are (at first glance) uncommon. Unscrewing the lens itself off a generic lens and moving the glass closer to the sensor shorten the multiplier.
And, as you will already have heard, good seeing is the biggest determinant (along with good collimation and focus) on what you will get. Good luck!
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