Headphone amps

I like to listen to music at night - my wife likes to sleep - I can't understand why she does this with so much good music to hear. Headphones have been a blessing for maintaining peace given our somewhat different nocturnal patterns. I'm soon getting a new integrated amp without a headphone jack, so I will require a little amp for the headphones. Please provide recommendations for headphone amps that you have used and loved. I like to listen to jazz and classical at night. I'm using a FMJ 23 as a source and I tend to like tube sound. I have Sennheiser HD 600 headphones.