Your vows can stay a surprise. For the sound check, a sentence from a book will do.
Read it at the volume you'd actually use during the ceremony, with someone listening from the back row. Ask them what you said. If they caught the beginning but lost the last few words, that's useful feedback for the person handling sound. A microphone tap or a song playing through the speakers won't give you the same information.
Stone Ridge's ceremony choices include the gardens, pergola and J&J's Tree. Once you've chosen your spot, share it and your seating plan with your DJ or sound provider. That's where the spoken check should happen. Mention any readings, too, especially if someone will speak from a different part of the ceremony area.
Arrange the check with them ahead of time so it fits into setup before guests arrive. You can talk through the plan at rehearsal, even if the wedding-day equipment won't be there yet.
Try it with the vow book
A microphone feels straightforward until you've also got a little book open in your hands. Who holds what? Where does the microphone go when it's your partner's turn?
Try the handoff with your officiant. Hold the book, turn a page, and read a few lines while facing your partner. Ask the person managing sound to show you where to keep the microphone as you move. It's a small thing to practice, and much easier to sort out before you're standing there in wedding clothes.
If you're both speaking, give both voices a turn in the check. The same goes for the officiant and anyone doing a reading. Let the DJ make the adjustments, then ask your back-row listener to listen again. If the seating spreads out to the sides, the DJ can suggest another place to check.
A guest's hearing needs deserve a separate conversation, too. If someone has told you they have trouble hearing, ask what helps them and discuss the options with the people handling the ceremony.
That first song as a married couple
The music at the end deserves a clear cue. Your officiant might have a few words after the kiss, or you might want to turn and face your guests before walking back down the aisle. Tell the DJ how you've pictured it.
The officiant, DJ and coordinator, if you have one, can agree on the exact words or signal that starts the recessional. “After the ceremony” leaves room for interpretation. “When the officiant says this line” gives the person at the controls something to listen for. The entrance music and its stopping point need the same quick conversation.
It's also worth confirming who is providing the ceremony equipment and who will run it. If that's your DJ, put the ceremony timing and cues in the notes you're already sharing with them. If someone else is doing it, make sure they have those details and know who to check with.
Then let them handle the sound. When it's time to open that vow book, you'll have better things to think about than where the microphone goes.