Re: raise solo level, lower background chords, or a mix
Some great pointers thus far aside from the ducking idea; sorry, but don't do that, it's a very bad idea to duck an entire mix in this contact. It works great for voice overs, but not for music production.
Assuming a) you are talking about mixing in the studio (live mixing is basically the same but the room has a much larger impact on what you hearing depending on where you are located in relation to the instruments) and b) that you have verified the issue on several monitors and not relying solely on one set of monitors as your room may be the actual issue, and not the mix at all --
Generally, all feature instruments, whether a guitar solo or vocal track, are treated the same way.
The first thing to do is make sure you are high pass filtering all of your tracks; masking ofter occurs when there is a buildup of low frequency 'mud' which also has harmonics that extend into the midrange frequencies.
The second thing you need to do is determine WHY the solo isn't cutting. Try raising the solo in the mix; if you find that solves the problem then you are done. If that doesn't solve the problem, then you need to listen VERY carefully to the guitar solo as you raise the fader; does it raise in level but still get lost (sounds both too loud AND too quiet at the same time)? Then you probably have a frequency clash somewhere. This is known as a 'stuck' fader.
If the guitar solo is panned center, and the rhythm guitars are panned left and right, they may be overlapping across the phantom center. Increasing the midrange of the solo and decreasing the same frequencies may not work in this case because you will lose definition on the rhythm guitars. One trick you can try is to apply an M/S EQ to the rhythm guitars and pan their upper mids to the sides; on the solo guitar use an M/S EQ and pan it's lower mids to the sides. This doesn't remove the critical mids from the guitars, it just clears up the center of the soundstage. (Waves' Center plugin works great for this technique). You can also use M/S EQ on the snare if it's the culprit.
The other culprits to look at are masking from the kick drum and bass guitar, often also panned dead center; these instruments can usually stand to have some cutting in the midrange to allow room for the lead guitar. You can automate those tracks so that they only apply the EQ during the solo if you otherwise like their balance within the mix.