As you must know Hindu philosophy believes God is both Nirgun (no attributes) and Nirakar (Formless) and also Sagun ( with all the attributes) and Sakar- (With Forms)....[Different schools of thoughts believe differently]
GOD is Formless and yet can take Infinite forms.... God has no attributes and yet He has ALL the infinite qualities...
But the vedas clearly state :
Ishwar ekoasti, Dwitiya naasti naasti naasti - God is one..... not two, not at all, not at all and not at all....
so there is no doubt that ultimately there is ONLY ONE GOD....
However the Vedas also state 'It started with ONE and then took to Infinite and again brought it to One having said "Neti Neti" means neither this neither that....'
So what is the connection between the NirGuna and SaGuna......One way of understanding that I like is through the formation of the the Five Elements...
From the Nirguna Bhraman came...
First Aakash - It has the quality of sound ....(OM sound)
From Aakash then came Vayu - which we can hear and feel (sound and TOUCH )
From Aakash and Vayu came Agni -which we can hear, feel and see ...( sound, touch and SIGHT)
Then from Aakash Vayu , Agni came Jal - which we can hear, feel, see and taste(rasa).... (sight , touch sound and FLAVOR)
From all them came the Earth which we can see, feel hear, taste and smell - ( sight , touch, sound, Flavor and SMELL)
So basically from the attribute-less Bramhan came all the 5 elements with their 5 gunas.....
Hence God although being nirgun and nirakar made all the qualities of Sight, Sound, Touch,Taste and Smell...hence He is also SAGUN and Sakar..
Hence the importance of Panch Tatva's....