IMHO, not enough gain in my Phono stage

The output of CD players is very high (2 watts) compaired to the 'classic' sources such as FM tuner (0.25 volts) and phono pre also 0.25 volts. (tape decks 0.25 volts too)
The odd and huge jump in output was right from the start of CD player production. Most likely to take advantage of the "louder is better" theory of marketing strategy.
You problem is thus normal! Everyone has to turn down the volume when going from LP to CD!!!!!!!!

Are you sure that you have a Denon 130, not a DL-160 or DL-110? If it is one of the later, the output is only 1.6mv, and although it is designed to be used into the MM stage of your phono preamp, most MM cartridges have an output of between 3.5 and 5.0mv., and most MM stages have a gain of around 40db. With the standard cartridges that your phono stage, and most other MM stages, are designed for, it would play somewhat louder. Actually, the excess gain of most tube based MM stages mates nicely with the Denon cartridges. At any rate, as others have said, just ignore it, if noise is not a problem, just keep twistin' that volume control.

Put an attenuator in the line from the CD player if the difference bothers you and you are not having noise problems. Otherwise the Creek 15 phono stage or at a higher price the ProJect Tube Box 11 SE.

You have mis-identified the issue. I would argue that your system has too much gain for your CD not too little for the phono. In an ideal world you would have the volume turned up to full blast just as it reached your desired volume level. Having the signal go through any volume control degrades the sound so the closer you have it to full volume the better the sound.

It sounds to me that you are using a passive linestage or a linestage with no gain or very little gain. I have a Rotel phono stage and when I used it with a linestage with no gain I experienced the same problem. My preamp is a VanAlstine Super PAS3si tube unit. I have since switched to a Hagerman Piccolo step up or headamp with gain settings and cartridge loading. It plugs directly into my tube preamps phono stage and all my problems with gain have been solved. With my existing phono stage having about 40db of gain the Hagerman gives me settings of 12, 20, and 30 db of additional gain. I choose the 12 db of gain and provides more than adequate volume.

I'm using an Audio Technica OC9II ML (0.4mv) with a Rega RB 600 tonearm. I have tried the 20db but the sound quality is better at the moment on the 12db and 100 ohms loading. I love that flexibility. If I play a record with lower gain and I need more I simply select the setting I want and in seconds MUSIC!

This was an example of how the linestage and gain play a role in the volume of your phono stage. The Rotel should be the gain of 40db MM or 5? or 60db for the Rotel PLUS the gain of your preamp or linestage.