In fact it would take quite a while to catalog all of the differences between these 2 amps. Although they are based on similar circuits, they are quite different in execution. Briefly, the DNA-2 design dates back to the mid '90s, just prior to the company's move to Virginia. The DNA-225 is much newer and incorporates a variety of improvements in circuit design and physical layout. The DNA-2 still has its fans, though, and at a conservative 300W per channel delivers a *lot* of power and authority. Only the new DNA-500 delivers more.
Please call me if you would like more detailed information.
Best regards,
Steve McCormack
www.SMcAudio.com