There is no low gain substitute for the M8080 ( 6C4 ) tube. I use this SCHIIT SYS to attenuate the output of my CDP. It’s worth a try!
If the problem exists with his Oppo 203 then the solution is to go into the set up option on the Oppo and set a max volume. This will enable him to run his CJ at a higher volume.@dover The wording in the manual for the Oppo UDP-203 pertaining to the "maximum volume" setting in the menu leaves me uncertain as to whether it (a) allows the entire output voltage range to be scaled down, or (b) simply limits the maximum possible output voltage. Do you know for a fact which of these possibilities applies?
If (b) applies your suggestion would of course not resolve the issue.
And if (a) applies do you have some idea of how much the maximum output voltage can be scaled down? I’m thinking that something like 0.5 volts would be necessary to satisfactorily resolve the OP’s issue, and preferably even less.
Regarding the other suggestions that have been offered, an advantage of an inline attenuator such as the one Imhififan suggested is that in contrast to the Sys it would not require an additional set of cables, and with it their potential to introduce sonic effects as well as adding cost.
As an alternative to the Harrison Labs attenuator the OP may want to consider Rothwell attenuators, either the 15 db version or the 20 db version. In addition to providing more attenuation than the Harrison Labs device they have a much higher input impedance (approximately 30K vs. a bit under 9K, both figures varying slightly depending on the input impedance of the device they are driving). In this particular case either input impedance appears likely to be suitable, but the low input impedance of the Harrison Labs device might limit its usefulness in the event of future changes to the system.
The Sys, btw, has an input impedance of only 10K, which like the Harrison Labs attenuator might make it unsuitable for use in the event of future changes to the system.
P.S: I neglected to mention that the approximately 30K input impedance I cited for the Rothwell attenuator applies to its 10 db version (and is based on measurements I have performed). But I suspect that the corresponding figure for the 15 db and 20 db versions is even higher.
Also, btw, the input impedance I cited for the Harrison Labs attenuator is based on measurements another member reported here a few years ago.
I originally purchased the SYS as I thought I needed it between the preamp and amp to be able to turn up the preamp volume control a higher amount. I then realized that my system was OK without it, i.e. that the volume control on my preamp could be turned up high enough without it.
I then happened to purchase a pair of monoblocks, and am using the tiny SYS as an enjoyable passive mini preamp, for two different sources. So for $49 + about $5 shipping you have a multiuse little gizmo.