I am not in this ball-park, but wouldn't it be best to sell off extra cards on the private market and then submit the lightest allowable 861 for the trade-in?
What is 'best' is an individual discussion.
1) Strip it to the bones, in an attempt to save a few �/$/Euro at the risk of alienating your local dealer.
2) Have a conversation with your local dealer and cut a deal with them. Thus maintaining a good relationship for the next purchase or support question.
3) Cut a deal with your local dealer for a non trade-in price; then see if you can sell it privately. If this is more than the trade-in deal you win a little but have the hassle and time scale of attempting to sell it privately.
Regards,
Carl