By Kirk Miller Great sound and innovative looks — just two reasons we’ve been big fans of Master & Dynamic. And whether you’re looking for an upgrade or a first-time user, today is your day: The upscale audio brand is hosting a sitewide 25% off sale. Launched in New York in 2014, M&D mixes eye-catching aesthetics with rich, warm acoustics. These aren’t headphones for DJs or fans of heavy bass, or for cheapskates. These are $250-$500 premium cans (or premium earbuds), and worth it — especially during this Friends & Family Sale. Unlike some past sales, there’s very little fine print here: You’ll…