I take Xanax for anxiety, I have pinched nerve in neck, what muscle relaxers are safe to take w/xanax and buspar (buspirone)?

Try a Neck Pro. Neck pro is an ingenious cerivical traction device developed by an er doc for his neck pain (usually the result of cervical disk disease or osteoarthritis). You can purchase this on amazon.Com for ~$60. Have used it myself and on multiple patients with excellent results. Don't use if you have osteoporosis or neurological symptoms. Works best on chronic pain. Sometimes on acute symptoms.
All additive. All muscle relaxants have sedative effects that are similar to Xanax so can have additive adverse effects. It might be better to replace the Xanax with the muscle relaxant temporarily. Discuss the conversion dose with your prescribers. The Buspar (buspirone) doesn't interact in the same way.