headphones for tube system

It may not be ideal but since it appears your pre-amp has neither a 'tape output' or a 'pass thru' you will need to get a headphone amp and connect it to the low gain output. The downside is that you will be stacking volume controls. I don't know of a headphone amp with out a volume control off hand, but you should research this - if one exists this could be ideal for you.

Thank you newbee - I'll certainly check that. As you note; most headphone amps have volume control.

Just unplug your CD player from the system, if it's not too complicated, and connect a headphone amp when you want to use it.  If your CD77 is out in the open it should be easy.  If the wires are buried, I give up.  
As to suggestions for headphones, you just have to listen.  I have the Grado GS1000, which are very open sounding, but totally not isolated.  You hear everything in the room, so you need quiet.  I tried some closed back phones, but they sound too closed-in for me, compared to the Grado.  You really need to check it out yourself.  Personally, I hate headphones for serious listening enjoyment.  Fine for Ipads and stuff, but, for me, not enjoyable at all.