Do I need a subwoofer for my audio physic sparks?

Does the Rogue have a preamp output/input? Some integrateds have this, where you can run the signal through an outboard processor (in this case, you would run it through the sub's crossover), and then back into the integrated's amplifier stage. If so, then look into a Vandersteen 2Wq sub, should work very well for you at a good price. I would normally recommend REL subs over the Vandys, but in your case, where you would like to take some load off the tube amp, you want a sub that has a high-pass filter built in.

If the Rogue doesn't have a preamp out/in loop, then you're pretty much stuck replacing either it or your speakers.

Oh yeah. Sparks need subs for full range stuff, if you want to go low, loud, or otherwise. That speaker wasn't designed to do deep bass well. Get a powered sub and be done wit it

The Rogue Tempest is as good as an integrateed gets. It is not your problem. Either get a Sub or a full range speaker.

You may also have cooked a driver. Try listening to one channel at a time and with a different amp if possible. It's fairly easy to roast an audio physic driver. I know of two people who have had this happen to them. If it's a harsh distortion, this may be the case.

You may also have noisy or worn out tubes. A tube amp should not 'break up' like a sold state amp. It should just have a soft distortion that kicks in when it runs out of gas. It will distort if you are REALLY overdriving the amp in which case you need a different speaker. If it's a warm, gradual breakup (like eric clapton's guitar sound), then it may be worn out tubes or insufficient power. I doubt you are out of power.

Also, look for loose connections. Sometimes these will only show up at higher volumes.

Sparks are fairly small voiced. Putting a more powerful amp on them will allow them to play the mid-upper range of music louder, but will not give you a large soundstage or bass. Sixty tube watts should be a plenty for them.

Adding a subwoofer will give you a larger soundstage and more power. It may solve your problem. Because of their speed I would only go with an audio physic subwoofer, specifically the Luna. You should be able to use a REL too. I tried a few subs with my Audio Physic Avanti's and the result was a laughable speed mismatch. You will likely spend $1500 used for a Luna. Hard to find used.

Another choice would be to upgrade to the virgo II. You can find those for around $2500. Those have excellent bass. You should be able to drive them with 60 tube watts, though 100 would be better. I drove my virgo's fairly well with a 45w CJ mv-50 amp. I once put a 45w ARC integrated tube amp on my avanti's and it drove them pretty well. My 100w vt100 was a better match though.