The 4430s are really
medium size speakers, and your dream has been to finally own some full-size speakers.
NO, don't tell her that!
Tell her you never thought you'd have the chance to own speakers like the 4435s and how much you appreciate the fact that she's not saying "Definitely not!" Tell her that you hope to get a good enough deal that there might be money left over after the transaction, and that as a sign of your appreciation you'd like to take her to a nice vacation spot for a weekend. Then suggest a really nice place (that you can afford), and let her react to it.
If she says "Yes," you're on your way.
If she reacts with a different choice, then says "Yes" you're on your way, because she told you what she wants.
(If she refuses to go, you're screwed, BTW.)
In either case, make her the focus of the entire weekend. Tell her
once (only once) during the weekend that you're thankful she's so understanding. Too many references to the JBLs will mess things up. Wine her, dine her, love her, pamper her, and take lots of pictures (not of the love making, though).
When you get back, determine which pictures she likes the most, then secretly get them enlarged, put them in nice frames that complement the 4435s, and place them on top. Yes, place them on top. (Put a cloth down first to dampen vibration and to protect the surface.)
Without saying any words about it, let her discover the pictures herself. If she brings it up (she will
), let her say what's on her mind and in her heart, keep your mouth shut, and hug her. From then on, everytime she fondly remembers the weekend and looks at the pictures, the bond between JBL 4435s and happiness will become stronger in her emotional matrix.