Will the Sansui provide enough power to drive the DT880 or HD-600 phones?
Yes, the Sansui will be able to deliver more than enough power from the headphone jack to power these or most any other dynamic headphones. The actual power available from the headphone jack is limited by the presence of in-line power dropping resistors and is in fact just couple of watts. Even 1 or 2 watts of power is many times the power needed to drive a pair of headphones. Most headphones require less than 30 milliwatts of clean power for full output. The HD-600 needs a bit more power, perhaps 100~200 milliwatts, but still far less than 1 watt for full output.
Will it do so properly?
That is something that each listener needs to decide for themselves. Many of the better vintage solid state amplifiers can perform very well as headphone amplifiers, comparable to dedicated amplifiers costing several hundred dollars ($200~$300).
A higher-end, and higher priced, amplifier can provide quieter background (less noise) and cleaner sound. This usually means giving up balance controls, tone controls, stereo/mono switching, and a phono stage preamplifier and being limited to only one or two high level inputs.
The Sansui would make a great starter amplifier and you can take the money would have spent on a headphone amplifier and buy more music or a better source (CD, vinyl, or one of the new higher-resolution digital format players (SACD and DVD-Audio)
