Da Tong Ren Du Er Mai
...means to open the ren and du meridians. They are the two main acupuncture meridians that run through the center of your body, front and back. Together they are called the small heavenly orbit or somesuch thing like that (xiao zhou tian).
Connecting them could mean to just touch your tongue to the roof of your mouth. Really they are already connected, otherwise you'd be dead. But different groups have different meanings for the same sets of words. Some refer to some great achievement in qigong and meditation, others just refer to it as being healthy, without impediments in your body.
"Tong" in Chinese means to be open, connected and without obstruction. You can think of it in terms of traffic on a highway. If everyone is travelling around I-495 without any problems, at 70mph, no congestion, no bottlenecks, and no traffic jams - that means that the traffic is "tong." On a highway, those bottlenecks, traffic jams and congestion mean stress, a slowing of the system, pain, problems, etc. Its the same thing in a human, if your system, your "qi," is blocked, or more precisely, bottlenecked, then you will experience problems as a result of it. Much of Traditional Chinese Medicine and its related practices aim to keep these highways thru your body open. Acupuncture, herbs, tuina, massage, qigong, exercise, eating properly all help to keep your meridians "tong."
One aspect of our bagua practice that we are shooting for is to keep our bodies "tong" or open - in terms of flexibility, freedom of motion, range of motion, health, the ability to bring our Yi to any point at any time, while not breaking good stucture and body movement, etc., etc. Like I've already said before, this is another reason we practice the longer motions in our forms (tiangan, xiantian, houtian, etc.) - to keep it open through the full range of motion. Some teachers will rail against too much fajing practice in forms for similar reasoning - it "shortens" your body's XXX (I don't know a good English word for this - I'd probably say yi or qi in Chinese).
But every type of training in martial arts has trade-offs to balance against something else. You balance training form against fighting, single movement practice against connected flowing practice, health against reality, weapons with open hand, going inside with outside, expansion with contraction, concentration with awareness, etc.
Anyways, I guess I started to ramble...
One big issue with many people is that they "think" too much and "feel" too little in their practice. Sometimes its better to just get hit in the head until you figure out a way to bring your hand up than it would be to analyze the angles and trajectories of the various paths created by potential attacks of an opponent and then intercepting those vectors of motion the proper response... well, you get the picture.
Or if it helps you more -
"Don't think! FEEL! It is like a finger pointing away to the moon... (thwack!) Don't concentrate on the finger or you will miss all that heavenly glory."
Ah, but I lapse.
Just practice. Don't worry, be happy. Circle on.