Is it necessary to use the same cable brand and model for bi-wiring??

Hi Jim,
I agree with adg101. I believe the benefits of bi-wiring likely become greater when running speakers with large, power-hungry low frequency drivers. For your Wharfdales, I would simply run those HT Pro 11+ cables, or your GHs, full range to the MF/LF terminals, use some high quality jumpers to the HF and enjoy the music.
I would consider using jumpers made with something like this:
http://www.partsconnexion.com/wire_hookup_neotech_cu_tef_sc.html
Since these are solid core wires, you can easily use a single wire without connectors as jumpers.
If you jump from the MF/LF posts to the HF posts, I would probably select the 16-18awg wire. If you jump from the HF posts to the MF/LF posts, then I would use the largest 12awg wire. Four 6-10 inch pieces should work just fine. They also offer the same OCC wire as stranded, which may be kinder to your HFs. You may need spades or banannas if you use the stranded wire.
http://www.partsconnexion.com/wire_hookup_neotech_cu_tef_st.html

Somewhat on topic. I just went to a bi-amp setup with my VR 33's and read in a review that the internal cabling of the speaker was Analysis Plus 14 gauge. Since I need new wire to replace my current bi wire cable (Morrow sp-5), I was wondering about cable matching to the internal wiring. Looking at the costs for some of the Analysis Plus cabling being sold here on Audiogon would there any benefit of much more expensive cabling outside connecting the speaker than there is internally? I could save hundreds but wouldn't realize what the actual difference would be without hearing both. Don't have much experience with system setups. Any feedback would be appreciated. Thanks.

As some have mentioned previously, talk to a dealer for ideas of cables that might sound good with your particular electronics and speakers.  I have owned various models of Vandersteen loudspeakers for the last 30 years.  His crossover networks are intended by design to be used with biwiring.  In conversations with the folks at Vandersteen they are quite emphatic that you not mix brands or cable topologies.  What I did to maximize quality and control the price of speaker cables to some extent was to buy two sets of Audioquest cables from the same "family".  The mid-high cable had the highest quality conductors and the bass cable was one step below in that family with slightly less pure conductors.  I am confident you could employ such a strategy with cables from numerous manufacturers.

Its best to use the same cable...as a matter of fact, its even better to bi-wire with seperate (but same) cable for each leg  (4 cables/side)  Cables that have single connection on one end and double (4) connections on the other are not as good.

Right on stringreen!