Depending on what you're used to in an amp, it's important to realize that the Recto series in general has long been noted for its lack of sustain, such as with a single held note in a solo. The accompanying problem is that it's also difficult to get natural even-order harmonics to feed back controllably. Both of these problems are really of the same origin...namely, that the Recto series has had to sacrifice some of the singing sustain and harmonics that come with a strong mid-frequency response curve in order to achieve the naturally mid-scooped sound and extra bass and low-mid response that the amps are famous for.
Going back to when the amps were first designed, Randall gets kudos for being prescient enough to create a monstrous new rhythm guitar amp, timed perfectly with the fact that, relatively speaking, lead guitar playing kind of dried up and fell out of favor in the 1990's. For rhythm, Randall's new Rectos crushed the Marshall JCM-800s they were meant to compete against, even though for soloing they never really quite matched up without external help. Rectos were never really geared toward being a lead player's amp. While it didn't much matter back then, today the concept of lead guitar playing has been slowly creeping back into hard rock/metal guitar playing again.
Players today don't want to give up the bone-crushing authority of their high-gain, mid-scooped, bass-heavy Recto amp to go back to a comparatively anemic stock JCM-800 kind of sound for rhythm. We're spoiled and who can blame us? However, we're starting to want a little more out of our amps in the soloing department again. We kinda miss the sustain, the tone that cuts through the mix when it's time for a solo, and the singing overtone harmonics that used to fly out of our Marshalls without much effort.
The solution that many of us who want to keep our Rectos have found (beside first and foremost learning to tweak your Recto correctly) is to assist it when it comes time for soloing with a few choice pieces of outboard gear.
Perhaps the most important is a good overdrive. Tastes vary, but most OD's will clean up some of the Recto's natural muddiness while adding in harmonic distortion and varying degrees of raw gain. Just adding a single high-quality overdrive and tweaking it correctly can give you all the 'lead amp' you need out of a Recto.
For those that want more, there are also clean boosts and treble boosters that can be added to the equation to taste. Whether for lead or rhythm, a good EQ in the effects loop is a simple way to gain a radical amount of control over your tone. For rhythm, cutting the 200Hz mud by @6db and possibly boosting the 100Hz thump by as little as 4db can completely solve the Recto's mud problem while giving it even more of the kind of chest-pounding bass you love.
For lead players, bumping up the 800Hz slider by 4-8db will bring back some of the singing overtones that Rectos are often missing on their own.
What's turning into a bit of a modern "classic" setup for Recto lead playing that I and others have helped popularize on this forum is to take a Tubescreamer-type overdrive, put it up front of the amp with the level maxed and the gain on zero, put an EQ in the loop with 200Hz slightly cut and 800Hz slightly bumped, and set your Recto's tone controls on channel 3 such that the presence is cut dramatically (even turned in all the way down in some cases), the treble and bass are both hovering around noon, and the mids are anywhere from noon to 2 o'clock to taste.
That setup, especially if you're playing loud enough to get the power tubes running nice and hot, will give you all the singing sustain your widdle heart desires. And if you want even more singing overtones than a Marshall could ever dream about, add a treble booster in front of the OD. Best of luck.
