My search has ended.

When purchasing new equipment it's important to carefully consider as many scenarios for it's use before taking the plunge.
My requirements, as I do a lot of theatre work, were for a keyboard that could quickly change sounds, provide some degree of control over extra sound modules, extra keyboards, when necessary and have at it's heart a killer piano sound and critically a keyboard action that was inspiring to play and reassuringly built to survive the rigours of gigging.

Enter the RD 700SX.

Sleek and robust it looks good. The internal architecture has been structured in such a way that access to important, favourite sounds is instant and there is great flexability for the user to organise the sounds to suit the needs of a particular song set or performance.
The piano sounds include two 88 note multi-sampled grand pianos, so no economical doubling up of samples here. They sound rich and wonderful over the entire key range.
The keyboard is expandable by adding up to 2 of the SRX series of expansion boards, which have their own dedicated front panel buttons.

Basic layout.

The keyboard allows four internal zones (which can all cover the entire key range) to be combined in any permutation with four external zones (controlling an external keyboard or sound module). There are extensive editing possibilities for all of these zones and four faders can provide either level control or alternatively control for other selected parameters.
It was surprising to see the depth of editing potential for the external zones. To list just a few: Midi out port, Channel, Bank/Programme, Volume, Pan, Reverb, Chorus, Mono/Poly, Transpose, Key range, Velocity response range, Attack/Decay/Release time offset, Cutoff/Resonance offset, Portamento etc. Some of these will no doubt respond differently depending on which external sound source is being communicated with, but the potential is there.
Of course the internal zones are equally flexible and the tones themselves allocated to these zones are tweakable and offer the inclusion of a selection of Reverb, Chorus or Delay and the choice of an interesting variety of 125 effects, including: Mic type/distance selection, Amp selection, Speaker simulation, Auto- Wah, Rotary cabinet, Flangers, Phasers, Auto panners, Slicer, Multi tap delays, etc. quite extensively editable themselves, which can be further refined on the fly, using dedicated front panel knobs.
There is an overall EQ section for the whole keyboard output, controlable from the front panel together with a switchable "Sound Control" parameter. This applies various editable types of dual band compression or frequency boost over the output of the entire keyboard.

One touch.

Now for performance ease Roland have provided "One Touch" buttons for your favourite Piano and Electric Piano sounds. Each will provide you with a choice of A or B. A fun, but practical touch in this mode is that the cursor buttons allow you to open or close the grand piano lid at various degrees, with the expected change of timbre that this produces and, yes, this is graphically portrayed in the image of the piano on the screen.
So whatever the current setup of the keyboard it's possible to switch instantly to one of these.
The individual tone select buttons can also be primed with your favourite selected sound for each category. There are overall 488 tones/sounds to choose from, including rhythm sets and standard GM2 tones.
Rhythm patterns and arpeggiation/phrase patterns are available to add some degree of auto accompaniment if that suits your needs, with dedicated rhythm/arpeggio buttons, as well as the ability to load in via USB Standard Midi Files and play them as songs.
All of the general settings/allocations can be stored as a Setup for recall. So you have at your fingertips the ability to recall from your favourite Piano/Electric Piano sounds plus the various allocations made to the tone select buttons, with their associated controllers & effects.
Or, alternatively, with the Numbers Lock function engaged, the tone select buttons become numerical input buttons and permit you to just dial up your required tone by it's tone number and play it on the currently selected zone.

Drawbar organ

If the tone selection is from one of the 10 drawbar organ models, (there are other organs as well) you have access to the drawbar screen. While here, the four faders operate the 9 drawbars and the speed of the rotary cabinet effect is flipped from a nudge of the pitch bend control.
You are able to add gritty drive and select the amp type.
They sound the business.

Overall impression.

My first impression was "At last, an instrument that has been well thought out for performance, with the added capacity for the external control that I need."
The keyboard touch/weight/velocity response is tweakable extensively and is a joy to play in it's consistency.
With it's complement of Midi In, 2 x Midi Outs, Midi Thru, USB, Damper Pedal socket, 2 x programmable footswitch sockets, Balanced outs on XLR's as well as Line outs, Headphone socket, 128 note polyphony, 16 part multi timbrality, it comes well equipped.
I was very soon navigating around the various screens, exploring the potential of the instrument.
The very "Open Architecture" of it's internal design allows great flexability to tailor this keyboard specifically to your own requirements.
The sounds, [with one or two exceptions, notably Pizzicato (Strings)] are remarkably good, especially, as one would expect in the piano/electric piano/organ departments.
To have everything else that this keyboard offers to hand as well gives me cause to rejoice.
I can at last start to leave the rack at home when gigging.

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Don't ya jus luvvit?

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