Are two smaller subs better than one larger?

If you know where to shop, you can get two $1200 subs for about $500, which should take good care of both HT and music. Go to vanns.com and do a search for Infinity subs.

I'm running dual subs in both my HT and 2-channel analog-primary stereo
rigs.

Generally speaking, I definitely like two smaller subs for stereo music. My
music-only subs are a pair of small (9" cube) Mirage MM-8 subs. They
are not for deep-deep bass; they're strong to about 35 Hz. But so many mid-
sized speakers aren't putting out real extension below 50-60 Hz, or
sometimes a small tower is in a slightly too-large room and can't put out the
low bass amplitude to occupy the space. That's where these small subs come
in. They totally occupy the 35-60 Hz zone, but best of all, the sealed
enclosures (with dual passive radiators), very high internal power (1200w
peak), high excursion surrounds and very light (aluminum) diaphragms make
for very "fast" woofers, with short rise times and quick settling,
making for an excellent blend with the light'n'lively 5-1//4" woofers in
my small towers. Plucked string bass is full and lush, yet quick and lively to
match fast bass passages.

The better Martin-Logan subs are also great at blending for music. Given that
their subs are intended to blend with their electrostatics, keeping up with
cones is pretty easy for them.

If you have the coin, I don't think you can do better than JL. A pair of F112s or
F113s would not only make the music come alive, they'll also give you true
strong bass down to 20 Hz with no bloat, resonant peaks, or overhang.

As much as I lean toward dual subs, I have heard excellent 2.1 sub setups.
Particularly I heard a pair of B&W PM1 minimonitors paired with one carefully
integrated wilkins.com/Speakers/Home_Audio/Subwoofers/PV1D.html>PV1D sub
and the resulting sound was seamless and transparent. The PM1s shined for
their even, timbre-correct tonality, seductive transparency, and stunning
imaging while the single PV1D sub supplied a foundation that completely
integrated with the stereo image from the pair of monitors. So it can definitely
be done.

In fact, that PV1D was a kick-ass sub and should be on your short list. Small
and fast, but goes deep and takes 2-channel input.

Rel isn't a cheap sub and nice sounding but 2 x Vandy 2Wq can beat that for less price paid than for single REL.