It would be much appreciated if someone could help me with the following query: I have a Marantz PM6005 amplifier. I'm planning to upgrade my headphones to Beyerdynamic DT880's. Ideally for classical music I need the semi-open version. However, these run on 600 ohm and Marantz technical support have suggested that I may need to get an headphone amplifier if running on 600. The headphones running on 250 ohm wouldn't need an amplifier but would be closed ear which aren't apparently as good for listening to classical music. So there seems to be a trade-off between sound quality and expense incurred in buying an headphone amplifier if needed. Thank you for taking the time to read all of this and I look forward to reading your comments and suggestions.