No headphone output....options???

Sorry if this is an obvious question. I searched but didn't find any answers. I have a Sophia EL34 integrated amp and I want to use my Sennheiser 600 with it, but there is no headphone output on the amp. Any suggestions? I know ASL makes a little box that runs $150 and goes in between the amp and speakers, having a headphone output and toggle switch. I'm hoping someone has another idea. Thanks.
Look for a headphone amp that has a pass through like a Channel Islands VHP1 headphone amp. You can put it between your integrated and source and listen either through your headphones or through your speakers without having to disconnect anything. I'm sure that there are other headphone amps with this feature, I mention the Channel Islands one because I'm using one with my Sennheiser 580s, a great combination. Good luck!
Yes, if there is a fixed line out on your Sophia (tape out), then you could connect a dedicated headphone amp to it. May not be the solution you want to hear, as your headphone listenting will not be benefiting from the glorious tubes.... but if this is a concern, there are various tube headphone amps out there for reasonable money, such as from Antique Sound Labs and Bottlehead.
I agree, puting a device in the signal path to your speakers is probably not a good idea, and a dedicated headphone amp is, IMHO, the best way to go for better sound.