Hello and I've just read your post hence the delay in replying.
I owned and loved a Yamamoto A011 (VT52) amp for nearly 9 years.
I've also listened to both the Yamamoto C03 with the 'normal' and stepped attenuators.
I have a few observations and opinions which you can follow or Ignore as you please. The A011 actually puts out about 1.8 watts, before clipping, as measured on a 'scope with load resistors, not 3 watts. It would simply not drive my Audio Note ANJ speakers at all! I did get a very quiet sound out of a pair of AN Es which are nearer 92db rather than 98db. I think you have to use this amp with a pair of easy-to-drive speakers of at least 100db. I have a pair of Lowther back-horn-loaded TP1 speakers which are 105db and play at rock concert levels with less than half a watt! The VT52 amp was brilliant with the TP1s BUT did hum in between tracks (less than 1mV hum) Speakers around the 100db mark will sound great and not have noticeable hum so are Ideal. So the likes of Klipsch Heritage Cornwalls or bigger. Maybe Zu audio speakers, Most Lowther BHL speakers, Avant Guard, or other speakers with an active bass?.
The Yamamoto CA03 is a very nice phono stage/pre amp. I've had to clean a friend's stepped attenuator CA03, a few times, to stop loud clicking noises caused by dc on the attenuator burning the contacts. The 'normal' attenuator CA03 doesn't have this problem and sounds just as good so that would be my choice (and it's a bit less expensive).
Oh and I still have a complete set of NIB and NOS valves for the VT52 amp
and the CA03 preamp, They would be for sale if you wanted them.