Want More Bass

Sub..VMPS Larger Subwoofer will solve your problems I think..

If you just changed amps, & are now bass-thin, isn't the problem obvious? Your speakers are obviously up to the task; they were working fine previously weren't they?
But if you're really stuck on keeping that amp, then try tweaking it. Tube roll. Try out different upgrade AC cords. Try different interconnects / speaker cables, for better synergy. Try shelving, cones, pucks, footers, & etc.
But forget the subwoofer!

Bob, I think your right about forgetting the sub woofer but for a different reason. One of his statements, that no one has keyed on, is his preference for low volume sound. One of the ancient studies about human hearing shows that we tend not to hear the presence of low frequencies at low volumes to the same degree that we hear the mid-range/highs. For a long time recievers and intergrated's included a tone contour control which implimented the Fletcher Munson curve (which has since been somewhat discredited - I believe because of the high end emphasis, not the low end). This provided for a increase in the bass which automatically diminished (the added emphasis) as the volume was increased until you had a flat frequency response signal at the output.

As I see it, if the poster adds a sub and tunes it for typical low volumes he'll be very unhappy when he increases the volume as the sub will then become overbearing. I'm not sure that full range speakers will make that much difference, but there are some full range speakers that do present a more balanced and resolved sound at lower volumes, however his room placements might make implementing full range speakers somewhat problematic.

Newbee,
I want to add to your thought about low volume listening and the KEY point in this case turs the AMP and the AMP only. Less-likely speakers are not rated conservatively and I feel the case is that speakers now don't even rich 65Hz and starve for more power.

Seems to me there are two key lines from the original post.

1. "(My current speaker's bass response is rated at 50hz.)"

So, based on their own rating, these speakers are missing the lower octave.

2. "Got a new Rogue Audio tube amp and preamp. (88 and 66 magnum). Used to have a solid-state integrated that seemed to have more bass output."

Here is a common complaint with regard to tube amplifiers,
they have a tendancy to be weak [or flabby] in bass. Tube
proponents often give up deep or tight bass for reputed
advantages in the sound of "tube mid-range."

Now, this brings up another point. Already, some posters
are counseling cable and power cord adjustments to give
this system more bass when the speakers themselves are
rated to only go to 50 Hz. This, IMO, is how people get
duped into blowing a lot of unneccessary money on cables.
Cables will not produce low bass in speakers that are not built to accomodate it.

Here is another key line from the original post:

3. "Used to have a solid-state integrated that seemed to have more bass output."

We can deduce that the former amp was better at maximizing
the speakers' bass down to its rated 50 Hz, while the tube
amp is having trouble.

The first thing I would advise is getting speakers capable
of producing the lowest octaves of bass, or as close as
possible given the price constraints. That's why I suggest
full range speakers.

Second thing; I would consider a change in amps. If the current amp is having trouble producing base down to 50 Hz
and you want more bass, I question whether you will be happy
with this amp.

3rd: It is nice to have a sub-woof for the lowest tones
and home theatre effects, but it is hard to find sub-woofs
that can do more than "thump." Further, it is hard to
tune them into the system unless you can set the crossover,
level, and phase perfectly.

For this reason, I also suggest getting full range speakers, to lessen your depedance on the sub-woof.

IMO, it is better to buy speakers with bass already integrated in a way you like, and there's a better chance
you will be happy with the crossover and phase, as well
as a better chance of having speakers that can make music
with the lower octaves rather than simply "thumping."

By all means, get a sub-woof -- after you find full range
speakers and an amp that can drive them. After you've
found a pair of speakers that can produce bass at least
into the mid-twenties, an amp that can drive them, and
a sub-woof that can give you detail and not just "thump" --
see if you still want to try to get wires to do this for
you instead of the components that are designed for and
capable of doing these things. If so, and you still have
money burning a hole in your pocket -- THEN -- experiment
with some wire and cable.

That's my suggestion.