A Roland Dimension D is going to be difficult to recreate with a single pedal or existing algorithm.  I've never owned one; just heard it.  It remains a mystery effect.  As I understand it, there's all manner of processing going on there.  It may help to do some of this sound shaping before/after it gets to to the H9:

Compander (noise reduction) circuit with some distortion added

Bass boost on just the dry signal

High pass filter before the delay signals (bass cut)

(No doubt) a low pass filter after the delays for the clocking frequency

Out-of-phase flattened triangle modulation of the L & R delays

Flipping of the stereo image on most switch positions

 

Then you add in the four switch options and combinations of each.  I've heard between 5 and 15 ms. of delay time; depending on the switch selected.  I don't know if any delay signal was fed back.  Modulation depth varies with each switch setting, and I'd stick with 0.25 – 0.50 Hz. for the modulation speed changes.  Very slow … almost imperceptible modulation rates.

That said, I've experimented with many of the H9 algorithms to this end.  Oddly enough, I never thought the Chorus variations were going to cut it (and I've yet to data-mine the PitchFactor algorithms for this).   Vintage Delay and Tape Echo have some advantages, but Mod Delay may be your best bet for coming close.

Here's something that I tossed together during the 5-minute demo at the Store.  It's a starting point that will need some serious tweaking.

Dimension D SW 1

Wet Mix = WET: 50

Delay Mix = A10+B10

Delay A = A:  5 ms.

Delay B = B:  6 ms.

Feedback A = 0 ms.

Feedback B = 0 ms.

(encoder) = Mod Delay / TMP: OFF

Mod Shape = ATRI B 180TRI

Mod Depth = 5

Mod Speed = 0.50 Hz.

Filter = (-) 25

Not too happy with the filtering results.  For different switch combinations, try increasing the delay times up to 15 ms.  Offset one delay time from the other by a millisecond or two (component variations, and it will sound thicker).  Of course, increase/decrease the Mod Depth with the Delay adjustments, and vary Mod Speed.  You should be able to emulate Dimension D switch positions with the HotSwitch, aux switches, MIDI, or even an expression pedal.