Objects with potential complements
First, 个 is not a classifier for 大米 , So I changed it to 些


There are only two potential particles for verbs.  


得 (able to) 
不 (unable to)



吃完 = eat all

吃[得]完 = [able to] eat all

吃[不]完 = [unable to] eat all


The placement of the object is flexible. When using [subject+ verb + object]sentence structure, the object is placed after the the verb, e.g. 我吃了米 (the verb particles 得 and 完 are part of the verb) 
The object can also be placed before the verb in passive voice sentences e.g. '米被我吃了' 
The object can also acts as the topic in [topic] + [comment] structure, and be placed at the beginning of the sentence.



  [S+V+O] sentence:
  
  [1. 我] [2. 吃] [3. 得] [4. 完] [5. 这些大米]
  
  [1. subject] [2. verb] [3. potential particle] [4. resultive particle ] [5. object]


It is very straight forward--  'subject' then 'verb' then 'object'.


  [Topic+ comment/opinion] sentence:
  
  [1. 这些大米] [2. 我吃得完] 
  
  [1. topic] [2.comment] 
  
  [这些大米(topic)] + [我吃得完(comment)]
  
  The object [这些大米] is the topic. the relative clause [我吃得完] is the comment.


Both examples above are grammatically correct. 


  [O+S+V] sentence (passive voice):
  
  [1. 这些大米] [2. 被][3. 我] [4. 吃] [5. 完] 
  
  [1. object] [2. passive marker] [3. subject] [4.verb] [5. resultive particle ]


We don't use passive voice with potential particle. Potential particle only works in active voice


[这些大米被我吃完] is grammatically correct
[这些大米被我吃得完] is grammatically incorrect



  Objects with potential complements


In summary: 


object must be placed after the verb in [SVO]  sentence, and potential complement is part of the verb.
object can be placed at the beginning of a sentence in [topic + comment] sentences.
in [OSV] (passive voice) sentence, we don't use potential complement