Cascade is different than Parallel. If you " jumper " the channels, you get a bigger tone ( than just a single input ) and a weeee bit more gain ( not much ), but can often take you from just not quite enough, to perhaps just enough.
With the cascade mod, you are running the tubes in series, or one into another, into another, etc. This adds significantly more gain and can take you from not enough, to more than enough gain.
Tit for tat, I like paralleled triodes as a method of producing gain. Done right, you gain about 3db of headroom, and therefore gain, you reduce the noise floor by nearly half, and it certainly adds a little more complexity to the sound. It usually sounds fatter, rounder, and more bubbly given the same relative gain structure as a single triode does. In my amp builds, a parallel triode is one of my things and is a primary characteristic of my designs.
Cascaded amp designs such as most Marshalls, are generally aiming for preamp-based distortion, or gain that is produced earlier in the amp. They tend to be less bassy, to keep the flub under control, reduce blocking distortion, and maintain a tighter sound. So some designs not designed with " cascading " in mind, can suffer from the added gain such a topology would acquire. It often requires more work elsewhere to tame the beast so to speak. Also, a thing to keep in mind is the added noise. Adding gain stages adds noise, and the lead dress and layout can interfere with the installation.
In my early amp design years, I struggled with trying to make an amp what it was not meant to be. I found that you have to design an amp around what it is. You can't just drop a JCM-800 preamp in a Vox AC30 and expect it to be a JCM-800, it doesn't work that way. Once I started thinking about the amp design as one step at a time, I realized you can end up taking the amp where it wants to go. Meanwhile, you learn how to manipulate your design to achieve your goal the first time around. I have a 5-watt design that is a prime example of that. I got it 95% of what I wanted on the first shot. Simple design granted, but, without having to update the design, I was at my target. The more complex the amp, the harder that is to achieve.
The point I am making is that I feel you should start with what doesn't disturb the original design too much. In this case, I think you should go with the parallel/jumper option. If that isn't what you are looking for, try going with a single channel of interest and then pushing it with a boost pedal. If that gets you where you want, then consider cascading. I would try a boost pedal with the first option anyway. Parallel triodes work really well with boost pedals.
