I'm also using the RX module as a SDR rx either standalone or as the IF for higher frequencies
This is what I did, it may help you or not.
First check you have actually I AND Q output. If one channel is not working you will get output but many "ghosts"
I removed the output transformers. There where big frequency dependent amplitude differences between the two transformers and I was unable to get to acceptable phase/amplitude balance.
I also remove the filter capacitors (R3-R6) and replaced them with 2.2nF capacitors to get a more flat output, minute differences between the original capacitors again made balancing the whole audio band impossible.