A 9 of pentacles type relationship to me is one where people are relaxed, content, a little older, happy to have time alone and to visit each other (the bird flies in and out) and still keep a full life outside of their partner. Having a beautiful garden, physical comfort and a lover who spends time with you could be a wonderful type of relationship. It makes me think of a confident couple where each has security and are relaxed in themselves. The opposite to needy if you like. It also suggests to me that the physical side of the relationship is important to these people. Where they live, sleep, sit how they touch, what they eat, what they do together are important for this relationship to thrive. Living in a hovel, eating beans on toast with no time apart would make this pair miserable. Comfort and some independence and enjoying the pleasures of life are what come to mind.
If the two of cups is describing the feeling (love returned equally) then the 9 of pentacles is describing the shape and substance of how this manifests. I think of pentacles as real physical realities, actions and in relationships, commitments. I don't see that one negates the other. In fact if I saw a love reading with no pentacles I wonder if there's anything solid about this relationship. Yes they may have all this feeling but what are they going to do about it? But I'm an earth sign so seeing positives in pentacles is easy for me. But I don't think its too much of a stretch to see cups and pentacles as suggesting love and commitment.