On the back you have the stereo outs (Jack), MIDI IN/OUT and THRU, a couple of inputs for Sutain Pedal and Continuous Controller and an expansion port for additional sounds (PCMCIA).
The synth is pretty loaded when it comes to sounds. It goes through all the genres and also includes a nice FX section (pretty good sounding Alesis algorithms). The synth has a 64-voice polyphony...very nice (of course that diminishes when you start using layers).
There is a PC/Mac port (serial) but don't bother. It didn't really work back then and surely doesn't work anymore today...this synthesizer came out around 1998!
I found programming the basic settings and using multi mode to be quite straightforward. Alesis has always been pretty good in making their equipment easily accessible. This synthesizer contains so many ways to vary a sound though that it is almost impossible to retain a certain overview with such a small display. This has been the problem with almost any synthesizer from that time (and even up to now!). If you spent some time with the instrument it is pretty easy to get the sound you want.
The manual explains the functions pretty well. So far every piece of equipment I bought from Alesis did supply me with a thought out and understandable manual - big props for that!
Here we get to the part of the QS 6.1 I don't like. The sounds are truly amazing by themselves and really you have such a huge amount to choose from it's ok to have some that are not really useful. The problem becomes apparent when you try to incorporate them into a bigger mix or make a MIDI arrangement. All of a sudden they all get washed out and none of these sounds really has a clear definition in a mix. The Grand Piano for example sounds great by itself (maybe a little harsh) but if you want to use it in a mix it is nowhere to be found.
The same goes for live applications by the way. This is the reason people use Roland. They often sound terrible by themselves - but if you need to cut through two guitars, drums, bass and voices then you will see why they are so popular. I think the sound of the QS 6.1 is great to sell it in the store but I have not been using it for years now because I just can't get them to work.
I really like the versatility of this synthesizer. The FX are very nice and a lot of the sounds are very inspiring. What I like the least I talked about above - and in the end...unfortunately...this is what makes me recommend an instrument or not.
I think for the price the QS 6.1 was a very good deal but looking back I would haven been better off in buying a Roland, Yamaha or Korg.