A dozen fairly simple approaches to this issue are listed below. For those of you who do not immediately perceive the connections between the following technical procedures and the installation, evaluation and adjustment of new audio equipment, I suggest the empirical approach -- try them, see whether they work for you, and use those which do.
1 -- Take your wife or girlfriend out to dinner or a movie about once a week. Ask her what restaurant or movie she wants to go to, and then go there without argument. Regardless of whether the food or the movie's plot are any good, tell her that you enjoy spending time with her.
2 -- Buy her flowers occasionally. Don't wait until you have ticked her off about something, and then try to make floral amends. Buy her flowers for no particular reason at all. You don't have to buy expensive ones, either. Just figure out what her favorite color is, buy flowers that color, put them in a vase with some water for her, and kiss her on the cheek or the back of her neck.
3 -- Even if she is an intelligent and professionally accomplished woman who is more than capable of handling auto maintenance on her own, keep an eye on the tire pressures and mileage of her car. When the tires need some more air, or it's due for an oil change, go take care of it yourself instead of telling her that she needs to do it. When you bring it back, tell her you just wanted to make sure that she was safe.
4 -- Do NOT buy her lingerie from a store with a catalog featuring airbrushed photos of surgically enhanced models under 25. Instead, buy her a good-sized gift certificate to a women's clothing store featuring attractive but not excessively stylish clothes whose prices are higher than she usually spends on herself. Express pleasure with and compliment the ensuing purchase.
5 -- If she looks upset about something, ask her what's wrong. Then shut up and just listen. Even if you disagree with what she says, even if it makes you so angry that steam comes out of your ears, just shut up and listen. When she is finished, don't respond. Just tell her you'll think about it. Then do think about it for at least a day before talking to her about it again.
6 -- When you're upset about something, don't tell her what a bad person she is, or how she always does this, that, or the other thing. Just tell her that it makes you unhappy when she does whatever it is, without casting aspersions on her motives or character.
7 -- Even if she doesn't look upset about anything at all, ask her occasionally how things are doing, and listen attentively when she tells you.
8 -- Ask her for some advice or suggestions about something, like how she thinks you ought to handle a problem with one of the kids, or how she wants to decorate one of the rooms, and let her know that you take what she says seriously. Try doing what she suggests, and then telling her how well it worked and what a good idea it was.
9 -- Sit down with her at some point to discuss the family budget, and reach agreement on some specific biweekly or monthly figure to be saved in a "toy account" for future purchases. Wait until you have enough money saved up in the account to pay for your next piece of audio equipment, so that you're not buying it on credit. Do your best to buy equipment whose price is reasonably proportional to other things in your life. (If your audio system costs more than the tuition, room and board at your oldest child's college, some reconsideration of priorities might be in order.)
10 -- If you're going to get a new piece of equipment, trying to sneak it in may be counterproductive. She'll probably notice anyway, and be annoyed even if she doesn't say anything about it. Tell her what you plan to get, and why. Unless she acts particularly interested or knowledgeable, keep the identification and explanation brief and non-technical. A couple of sentences in plain English is good. Multiple paragraphs in technobabble is bad. Make sure that she knows that the money to pay for it is coming out of the "toy account," and that there's enough in there for it.
11 -- Exercise self-restraint regarding the number, scope and cost of structural modifications which you make to your primary residence for reasons of acoustical improvement or oscillatory damping. Remember, they've rebuilt Avery Fisher Hall at Lincoln Center several times now, and they still don't have the acoustics quite right. If Bolt, Beranek & Newman couldn't make one of the premier concert halls in the country come out perfectly, your chances of accomplishing better results with fewer resources may be somewhat limited, and your spouse doesn't sleep in Lincoln Center every night.
12 -- If your wife or girlfriend is accepting, interested, knowledgeable about or involved in audiophile equipment, and willing to sit with you and listen to music on your equipment, you should go to church on Sunday (or schul on Shabat, or your personal equivalent) without further delay and express your gratitude for the unusual blessings which have been bestowed upon you by the grace and generosity of your benevolent Creator.
